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BEHAVIOR  MONOGRAPHS 


Volume  2,  Number  6,  1915 


Serial  Number  1 1 


Edited  by  JOHN  B.  WATSON 

The  Johns  Hopkins  University? 


The  Effect  of  Age  on  Habit  Formation 
in  the  Albino  Rat 


DISSERfAliON 

Submitted  to  the  Board  of  University  Studies     f  the  Johns  Hopkins 

University ,  in  conformity  with  the  re  ;uirements  for  the 

Degree  of  Doctor  of  Philosophy 


BY 

HELEN  B.  HUBBEHT 
1915 


Published 

at  Cambridge,  Boston,  Mass. 

HENRY  HOLT  &  COMPANY 

34  West  3M  Street,  New  York 

G.  E.  STECHERT  &  CO.,  London,  Pari«  and  Leipzij,  Foreiga  Agenta 


EXCHANGE 


BIOLOGi 

LIBRARY 

G 


THE  EFFECT  OF  AGE  ON  HABIT 

FORMATION    IN    THE 

ALBINO  RAT 

DISSERTATION 

Submitted  to  the  Board  of  University  Studies  of  the  Johns  Hopkins 

University,  in  conformity  with  the  requirements  for  the 

Degree  of  Doctor  of  Philosophy 


BY 
HELEN  B.  HUBBERT 


BALTIMORE,   MARYLAND 
JUNE.    1915 


H? 


BIOLOGY 

LIBRARY 

G 


CONTENTS 

Page 

•Acknowledgments v 

Introduction 1 

Historical 1 

Apparatus  and  Procedure 4 

Experimental  Results: 

Twenty-five  day  rats 15 

Sixty-five  day  rats 23 

Two  hundred  day  rats 29 

Three  hundred  day  lats 33 

Five  hundred  day  rats 38 

Comparison  of  Results  for  Different  Ages 42 

Incidental  Tests: 

Effect  of  Sex  on  Rapidity  of  Learning 46 

Day  and  Night  Work ; .  47 

Continuation  of  Work  after  Problem  has  been  Learned 48 

Blood  Relationship  and  Learning 51 

Retention 52 

Resume  of  Conclusions . .  54 


iii 


ACKNOWLEDGMENTS 

The  writer's  heaviest  obligation  is  to  Professor  John  B.  Wat- 
son, Director  of  the  Psychological  Laboratory  of  The  Johns 
Hopkins  University,  without  whose  unsparing  suggestions  and 
criticisms,  the  work  could  not  have  been  brought  to  a  successful 
conclusion. 

Dr.  Knight  Dunlap,  Associate  Professor  of  Psychology  at 
The  Johns  Hopkins  University,  offered  much  needed  assistance 
in  the  handling  of  the  data. 

Dr.  Gardner  C.  Basset,  of  Pittsburgh  University,  gave  valu-  * 
able  suggestions  regarding  technique  and  method. 

Dr.  Henry  H.  Donaldson  of  The  Wistar  Institute  of  Anatomy, 
furnished  practically  all  of  the  rats  used  for  breeding  purposes 
as  well  as  a  few  of  those  employed  in  the  experiment,  and  was 
most  helpful  in  suggestions  throughout  the  experiment. 

Dr.  Shinkishi  Hatai  of  The  Wistar  Institute  of  Anatomy,  pre- 
pared anatomical  data  for  each  rat  used  in  the  experiment, 
which  cannot  be  adequately  handled  in  this  discussion,  and 
which  will  probably  be  taken  up  in  a  separate  publication  to 
appear  later. 


THE  EFFECT  OF  AGE  ON  HABIT  FORMATION 
IN  THE  ALBINO  RAT 

INTRODUCTION 

The  present  investigation  is  concerned  with  the  problem  of 
the  relation  of  the  age  of  an  animal  to  its  learning  capacity. 
Experiments  were  begun  in  the  Psychological  Laboratory  of 
The  Johns  Hopkins  University  during  the  winter  of  1912,  and 
continued  until  the  spring  of  1915. 

HISTORICAL 

So  far  as  the  writer  has  been  able  to  ascertain,  practically 
no  prolonged  experimental  work  has  been  undertaken  hitherto 
on  the  relation  of  age  to  learning  ability,  although  the  import- 
ance of  the  problem  has  been  generally  conceded. 

In  the  field  of  human  psychology,  Munn1  carried  out  a  series 
of  "  substitution  tests  "  on  children  in  the  grades,  on  normal 
school  pupils,  and  on  two  elderly  persons,  to  determine  the 
relative  rapidity  of  gain  in  ability  to  make  the  required  sub- 
stitutions. Her  records  were  taken  in  the  terms  of  time,  and 
showed  that  although  the  children  gained  much  more  rapidly 
than  the  adults,  their  actual  rate  of  speed  at  the  beginning 
was  lower,  and  that  they  did  not  reach  the  same  level  of  effi- 
ciency within  the  limits  of  the  experiment.  Only  two  elderly 
subjects  were  used,  hence  too  much  reliability  cannot  be  at- 
tributed to  the  results  from  the  last  group,  but  apparently, 
while  their  initial  rate  is  intermediate  between  that  of  the 
children  and  the  normal  school  pupils,  they  fail  to  reach  the 
final  rate  attained  by  either  of  them.  Munn  gives  neither  the 
average  nor  the  rate  of  gain  for  this  last  group,  but  the  former 
was  easily  obtained,  and  appears  in  the  table  below. 

Adults  —  first  test    42  seconds  —  last  test  14  seconds 

Children         —  first  test  184  seconds  —  last  test  32  seconds 
Old  persons    —  first  test    72  seconds  —  last  test  39  seconds 

1Munn.    Curve  of  Learning.     Archives  of  PsychoL,  no.  12    p.  37. 

1 


HELEN  B.  HUBBERT 


Gain  in  first  5  tests: 

Adults  16  seconds  Children  34  seconds 

Gain  in  second  5  tests: 

&  Adults  5  seconds  Children  14  seconds 

It  would  appear  from  these  results,  that,  if  the  rate  of  improve- 
ment is  the  question  considered,  children  learn  about  twice  as 
fast  as  adults. 

Turning  to  the  field  of  animal  behavior  we  find  a  somewhat 
larger  amount  of  experimental  work  on  the  matter  under  dis- 
cussion, although  practically  all  of  it  occurs  as  a  side  issue  to 
some  other  problem.  Slonaker2  undertook  a  study  of  the  nor- 
mal activity  of  the  white  rat  at  different  ages,  hoping  to  "  ascer- 
tain how  the  age  of  greatest  activity  compared  with  that  at 
which  the  rats  were  most  capable  of  education."  His  con- 
clusions which  relate  particularly  to  the  subject  of  this  discus- 
sion are  as  follows: 

1.  "  White   rats  of  different   ages   show  a  marked  difference 
in  their  activity. 

2.  "  The  very  young  rat  and  the  very  old  rat  are  each  notice* 
ably  inactive. 

3.  "  These  experiments  indicate  that  the  age  of  greatest  activ- 
ity ranges  between  87  and  120  days. 

4.  "  From  these  preliminary  experiments  no  correlation  can 
be  made  between  the  age  at  which  they  are  most  active  and 
the  age  at  which  they  learn  most  rapidly." 

In  a  later  paper3  he  places  the  age  of  greatest  activity  for  the 
males  at  three  hundred  days,  and  for  the  females  at  three  hun- 
dred and  seventy-five  days.4  The  daily  activity  increases  with 
the  advance  in  age  until  a  certain  age  is  reached,  after  which 
there  is  a  gradual  reduction  till  death  occurs.8  "  The  female 
is  much  more  active  than  the  male."6  There  is  seen  to  be  a 


2  Slonaker,  J.  R.    The  Normal  Activity  of  the  White  Rat  at  Different  Ages. 
Journ.  Comp.  Neur.  and  Psych.,  17  ('07),  342-59. 

3  Slonaker,  J.  R.    The  Normal  Activity  of  the  Albino  Rat  from  Birth  to  Nat- 
ural Death,  etc.    Journ.  Animal  Behav.,  II  ('12),  20-42. 

4  Op.  cit.,  p.  30. 
6  Op.  cit.,  p.  26. 
6  Op.  cit.,  p.  42. 


HABIT  FORMATION  IN  THE  ALBINO  RAT  3 

discrepancy  in  the  results  of  the  two  papers  which  Slonaker 
does  not  attempt  to  explain.  In  the  latter  paper  as  in  the 
earlier  one  no  attempt  is  made  to  correlate  amount  of  activity 
with  capacity  to  learn. 

Yerkes7  raised  the  question  of  the  relation  of  age  to  habit 
formation  in  the  dancing  mouse.  He  worked  first  on  the  ac- 
quisition of  the  white-black  discrimination  habit,  and  later  on 
the  learning  of  simple  labyrinth  pathways.  The  indices  of 
modifiability  as  given  by  the  number  of  training  tests  required 
to  complete  the  habit  for  dancers  of  one  and  four  months  re- 
spectively show  that  the  males  learned  the  white-black  dis- 
crimination habit  more  quickly  at  one  month  (30  days)  than 
at  four  months  (120  days)  while  the  reverse  was  true  of  the 
females.8  The  female  was  superior  to  the  male,  however,  in  the 
formation  of  the  labyrinth  habit.9  In  later  work10  he  finds 
that  male  dancers  ten  months  old  learn  the  labyrinth  more 
rapidly  than  those  one  to  two  months  old,  while  there  is  prac- 
tically no  difference  in  rapidity  of  learning  of  one  to  two  month 
and  ten  month  females.  The  old  dancers  are  somewhat  superior 
to  the  young  in  their  ability  to  learn  the  labyrinth  paths.11 
With  regard  to  the  sensory  habit  he  says: 

"  1.  The  dancer  at  one  month  of  age  acquires  a  particular 
white-black  visual  discrimination  habit  more  rapidly  than  do 
older  individuals.  From  the  first  until  the  seventh  month  there 
is  a  steady  and  marked  decrease  in  rapidity  of  habit  formation; 
from  the  seventh  to  the  tenth  month  the  direction  of  the  change 
is  reversed.  These  statements  hold  for  both  sexes. 

"  2.  Young  males  acquire  the  habit  more  quickly  than  young 
famales,  but  between  the  ages  of  four  and  ten  months  the  fe- 
males acquire  the  habit  the  more  quickly."12 

Haecker,13  in  work  on  the  Mexican  axolytl,  found  that  the 
habit  of  distinguishing  between  wood  and  meat  when  offered  to 
the  animals  in  forceps,  was  learned  with  far  greater  difficulty 

7  Yerkes,  R.  M.    The  Dancing  Mouse.    The  Macmillan  Co.,  1907. 

8  Op.  cit.,  p.  274. 

9  Op.  cit.,  p.  273. 

10  Yerkes,  R.  M.    Modificability  of  Behavior  in  its  Relation  to  the  Age  and 
Sex  of  the  Dancing  Mouse.    Journ.  Comp.  Neurol.  and  Psychol.,  19  ('09),  237-271. 

11  Op.  cit.,  pp.  266-267. 

12  Op.  cit.,  p.  269. 

13  Haecker.     Arch.  f.  d.  ges.  Psych.,  25,  1-35. 


4  HELEN  B.  HUBBERT 

by  the  young  (nine  month)  individuals  than  by  the  old  ones, 
whose  age  is  not  given. 

Watson14  in  his  Animal  Education,  discusses  work  both  on 
habits  involving  simple  motor  ability  and  on  those  requiring 
skill  in  manipulation.  He  concludes  that  "  a  young  rat  will 
solve  for  the  first  time  more  quickly  than  a  mature  rat  any 
problem  conditioned  on  mere  random  activity,  but  that  a  prob- 
lem involving  associative  activity  and  manipulation  is  more 
easily  solved  by  the  older  animals."  He  found  that  with  the 
simple  saw-dust  box  the  average  time  of  entrance  for  the  old 
rats  was  85.50  minutes,  while  that  for  the  young  ones  was  6.87 
minutes  and  says  further,  "  there  is  a  gradation  in  the  number 
of  useless  movements  made  by  rats  at  different  ages.  At  thirty- 
five  days  of  age,  when  physical  activity  appears  to  have  reached 
its  highest  stage,  the  percentage  of  useless  movements  is  largest. 
As  the  rats  grow  older,  this  stiperabundant  activity  disappears, 
and  in  its  place  comes  direction  of  activity." 

To  summarize  the  main  points  in  this  brief  historical  survey, 
we  may  note: 

First: — That  there  is  disagreement  as  to  the  age  of  greatest 
activity,  Slonaker  putting  it  first  between  eighty-seven  and  one 
hundred  twenty  days,  and  later  at  ten  months  for  the  males 
and  twelve  and  a  half  months  for  the  females,  while  Watson 
believes  it  to  be  at  about  thirty-five  days; 

Second: — That  Yerkes  finds  the  labyrinth  habit  more  easily 
learned  by  the  old  dancers  than  by  the  young,  while  if  Watson's 
interpretation  is  correct  the  reverse  should  be  true; 

Third: — Yerkes  concludes  that  the  female  is  superior  to  the 
male  in  learning  the  labyrinth. 

APPARATUS  AND  PROCEDURE 

Albino  rats  were  chosen  as  subjects  in  this  investigation,  for 
several  reasons:  Slonaker,  Watson  and  Yerkes  worked  with 
rodents,  and  we  desired  to  compare  our  results  with  theirs. 
Nearly  two  hundred  animals  were  required  for  actual  experi- 
mental work  and  many  more  than  that  had  to  be  kept  on  hand 
to  provide  for  replacing  any  which  might  become  unfit  for  work, 
and  to  allow  for  the  usual  losses  through  death  and  sickness. 
It  has  been  found  that  white  rats  are  easier  to  breed,  handle, 

"Watson,  J.  B.    Animal  Education.    University  of  Chicago  Press,   1903. 


HABIT  FORMATION  IN  THE  ALBINO  RAT  5 

and  care  for  in  large  numbers  than  any  other  small  mammal. 
For  reasons  which  will  appear  later,  we  adopted  the  circular 
maze  as  our  problem  since  it  is  generally  conceded  that  the  rat 
is  pre-eminent  among  animals  in  his  ability  to  thread  a  labyrinth, 
while  his  satisfactoriness  as  a  subject  for  experimental  work 
is  attested  by  the  number  of  experimenters  who  have  employed 
him  in  various  capacities. 

The  rats  were  bred  in  our  own  laboratory  as  needed,  inbreeding 
being  carefully  avoided  and  all  possible  care  being  taken  to 
maintain  uniformity  of  breeding  conditions.  All  of  the  rats 
were  weaned  at  from  eighteen  to  twenty-three  days,15  and  the 
sexes  were  separated  at  thirty-five  to  forty  days  and  kept  sepa- 
rate thereafter.  The  living  cages  were  protected  from  mice  and 
gray  rats  by  screened  compartments  constructed  of  pine  and 
one  fourth  inch  wire  mesh.  Every  two  weeks  the  cages  were 
thoroughly  cleaned,  the  shelves  washed  with  a  disinfecting  solu- 
tion, and  the  rats  dipped  in  a  one  per  cent  solution  of  "Kreso" 
to  prevent  the  rise  and  spread  of  vermin.  The  animals  were 
carefully  watched  and  treated  immediately  upon  the  appear- 
ance of  parasites,  so  that  they  were  kept  continually  in  a  healthy 
condition.  The  diet  consisted  of  milk-soaked  bread  given  every 
day,  and  a  mixture  of  cracked  corn  and  sun-flower  seed  every 
other  day.  They  seemed  to  thrive  on  this  somewhat  restricted 
diet,  so  that  no  additions  were  made  to  it  although  both  Basset 
and  Ulrich  used  carrots  and  fruit  occasionally. 

The  rats  were  handled  freely  from  birth,  and  consequently 
were  perfectly  tame  and  evinced  no  fear  of  the  experimenter. 
Special  care  was  taken  to  tame  any  rat  seeming  a  little  wild, 
before  beginning  work  with  him;  since  it  was  believed  that  fear 
and  timidity  might  cause  irregularities  in  behavior,  a  belief 
which  was  substantiated  during  the  course  of  the  experiment. 

It  was  desired  in  this  work  to  obtain  not  only  a  record  of 
time  but  also  a  distance  record  of  the  learning  process,  since 
it  was  felt  that  this  might  throw  considerably  more  light  on  the 
factors  involved  in  learning  than  had  yet  been  obtained.  The 
maze  problem  seemed  to  offer  greater  possibilities  in  this  line 
than  either  sensory  problems  requiring  a  long  and  tedious  course 
of  preliminary  training,  or  problems  of  manipulation  permitting 

15  No  bad  effects  were  noticed  from  this  early  weaning  and  the  rats  were  found 
to  be  extremely  active  as  early  as  the  sixteenth  day.  See  Slonaker,  op.  cit.,  p.  350. 


6  HELEN  B.  HUBBERT 

of  movements  in  two  dimensions  which  would  be  practically 
impossible  to  trace.  We  therefore  selected  as  our  problem  the 
learning  of  the  circular  maze. 

Heretofore,  the  only  data  possible  on  such  a  problem  have 
been  in  terms  of  time  and  errors,  the  time  being  the  only  reliable 
record  since  it  is  practically  impossible  to  evaluate  and  stand- 
ardize errors.18  With  regard  to  this  Miss  Hicks  17  says:  "The 
prevalent  practice  of  omitting  all  total  and  partial  returns  from 
the  error  record,  and  of  making  no  attempt  to  evaluate  varying 
degrees  of  error  gives  a  curve  which  is  not  only  worthless  but 
false."  She  says  further:  "The  total  distance  criterion  pre- 
sents so  many  difficulties  as  to  render  it  impracticable  for  ordi- 
nary work.  One  difficulty  lies  in  the  matter  of  taking  records 
accurately.  The  rats,  after  a  few  trials,  run  so  rapidly  that  it 
is  extremely  difficult  for  one  person  to  observe  and  record  at 
the  same  time.  To  do  this,  it  is  necessary  to  mark  off  the  maze 
into  small  segments  and  commit  to  memory  some  scheme  of 
representation  so  that  records  can  be  jotted  down  in  a  purely 
automatic  manner.  The  work  of  transcribing  this  record  into 
distance  terms  and  computing  the  same  is  very  laborious. 
Eliminating  these  practical  difficulties,  the  distance  criterion  is  in 
some  ways  an  ideal  one.  (italics  mine.)  There  can  be  no  diver- 
gence of  practice  as  to  what  shall  be  omitted  or  included  and 
results  obtained  by  different  experiments  upon  the  same  maze 
will  be  strictly  comparable."  "  The  distance  and  error  criteria 
are  fundamentally  alike.  The  distance  curve  is  the  better  repre- 
sentative of  the  progressive  approximation  of  the  act  towards 
automatic  accuracy.  It  portrays  all  the  details  of  this  elimina- 
tive  process  and  it  approximates  the  ideal  of  uniformity  and 
regularity  of  descent.  However,  it  is  impracticable  from  the 
standpoint  of  recording  and  manipulating  the  data." 

These  practical  difficulties  in  "  recording  and  manipulating 
the  data  "  have  been  overcome,  at  least  where  small  animals 
are  the  subjects  used  in  the  maze.  The  total  distance  can  be 
obtained  accurately  by  means  of  the  camera  lucida  attachment 
designed  by  Professor  Watson  (see  Fig.  1)  for  use  with  his 

"Watson,  J.  B.  Noddy  and  Sooty  Terns.  Carnegie  Pub.,  no.  103,  p.  249, 
note  1. 

17  Hicks,  V.  C.  The  Relative  Values  of  Different  Curves  in  Learning.  Journ. 
Animal  Behav.,  I,  138-156. 


HABIT  FORMATION  IN  THE  ALBINO  RAT  7 

circular  maze.  This  maze  has  a  wooden  base  one  hundred  and 
fifty  centimeters  in  diameter  and  six  aluminum  runways  fifteen 
and  five  tenths  centimeters  high  and  ten  centimeters  wide. 
The  entrances  to  the  alleys  are  ten  centimeters  wide,  and  are 
at  alternate  ends  of  a  quadrant  arc.  The  radial  stops  in  alleys 
1  to  5  are  also  placed  at  alternate  ends  of  a  quadrant  arc,  the 
stop  in  each  alley  being  directly  opposite  its  entrance.  Thus, 
it  is  possible  for  a  rat  to  run  only  one  half  the  circumference 
of  a  runway  in  either  direction  before  being  forced  to  turn. 
This  is  not  true  of  alley  6,  where  no  stop  is  employed.  The 
central  circle,  or  food  compartment  is  twenty  centimeters  in 
diameter.  A  three  quarter  inch  mesh  wire  top  prevents  the 
animals  from  escaping,  without  interfering  with  observations  of 
their  movements.  The  camera  lucida  attachment  consists  pri- 
marily of  two  mirrors  and  an  achromatic  lens.  The  arrange- 
ment is  as  follows:  A  large  plate  glass  mirror  is  fastened  by 
supporting  framework  at  an  angle  of  forty-five  degrees,"  with  its 
center  directly  above  and  one  and  eight  tenths  meters  from 
the  center  of  the  maze.  A  somewhat  smaller  mirror  is  placed 
facing  the  first  and  making  an  angle  of  ninety  degrees  with  it 
at  such  a  distance  away  that  the  light  reflected  downward  falls 
outside  the  maze  area.  In  the  path  of  this  reflected  light  is 
placed  a  single  achromat  six  centimeters  in  diameter  and  of 
fifty  centimeters  focus  in  a  mounting  provided  with  rack  and 
pinion  adjustment  which  is  fitted  into  the  center  of  a  wooden 
disc  thirty  centimeters  in  diameter.  Below  this  at  the  focus  of 
the  lens  is  placed  a  second  wooden  disc  of  the  same  diameter  as 
the  first,  which  serves  as  a  holder  for  the  paper  upon  which 
the  image  of  the  maze  is  reflected.  Both  of  these  discs  are 
attached  to  iron  collars  which  slide  independently  up  and  down 
the  rod  CR,  thus  making  it  possible  to  vary  the  size  of  the 
image.  A  small  curtain  of  dull  black  velvet  attached  to  the 
upper  disc  serves  to  exclude  all  extraneous  light  from  the  re- 
cording table  and  as  a  further  aid  in  sensitizing  the  eye,  a  large 
curtain  of  dark  material  encircles  the  space  occupied  by  lens 
and  recording  apparatus  as  well  as  the  experimenter's  chair. 
This  curtain  also  serves  the  purpose  of  completely  hiding  the 
experimenter  from  the  animals  while  they  are  running  in  the 
maze. 


HELEN  B.  HUBBERT 


FIGURE  1    Maze  with  Watson  Camera  Lucida  Attachment 

Illumination  is  obtained  by  means  of  six  40-watt  tungsten 
lamps  placed  symmetrically  around  the  maze  and  one  150-watt 
tungsten  in  the  center.  These  lights  are  mounted  on  brass 
rods  and  fitted  with  aluminum  shades  blackened  on  the  upper 


HABIT  FORMATION  IN  THE  ALBINO  RAT  9 

surface.  The  central  shade  is  circular,  those  for  the  peripheral 
lights  are  half  shades. 

The  floor  of  the  maze  is  covered  with  white  linoleum,  which 
can  be  thoroughly  scrubbed  whenever  necessary.  The  entrance 
to  the  starting  box  is  supplied  with  a  hinged  door  which  can  be 
securely  fastened  after  the  animal  has  been  placed  inside.  The 
exit  is  provided  with  a  sliding  door  which  is  raised  by  means 
of  a  cord,  and  closes  of  its  own  weight  when  the  tension  on  the 
cord  is  released,  thus  making  it  impossible  for  a  rat  to  return 
into  the  starting  box  after  it  has  once  entered  the  maze.18 

By  means  of  the  two  mirrors  (M  and  M'),  and  the  lens  (L), 
an  exact  image  (I  M)  of  the  maze  is  thrown  on  the  recording 
table  where  the  experimenter  can  follow  every  movement  of  the 
animal  during  any  passage  through  the  maze.  Actual  records 
of  these  trips  are  made  by  tracing  on  the  record  sheet  with  a 
soft  pencil  the  successive  movements  of  the  rat.  (See  Fig.  2). 
These  tracings,  measured  with  a  chartometer  shown  by 
calibration  to  be  accurate  to  within  one  per  cent,  form  the 
basis  for  the  distance  record.  Since  the  maze  is  six  and  four 
tenths  times  as  large  as  the  image,  the  distance  record  obtained 
in  centimeters  by  the  chartometer,  must  be  multiplied  by  six 
and  four  tenths  to  obtain  the  actual  distance  traversed  in  the 
maze.  For  example,  if  the  distance  indicated  by  the  char- 
tometer is  one  hundred  and  twenty-one  centimeters  we 
obtain  the  actual  distance  run,  thus,  121  centimeters  x  6.4  = 
774.4  centimeters.  The  values  given  in  the  tables  represent  the 
actual  distance  covered  by  the  rats.  Both  chart  and  maze 
distances  were  tabulated,  and  the  multiplications  made  to  ob- 
tain the  latter  were  checked  on  the  adding  machine.  In  addi- 
tion  to  the  distance  record,  such  charted  pathways  also  furnish 

18  The  maze  was  used  exactly  as  described  above  throughout  the  work  in  order 
to  maintain  the  same  experimental  conditions  for  all  the  groups.  However,  in 
the  course  of  the  experiments,  several  possible  improvements  suggested  them- 
selves as  being  desirable: 

First. — The  maze  should  be  constructed  of  such  material  that  it  could  be  frequently 
flushed  out  with  a  hose,  and  a  plug  should  be  fitted  into  the  bottom  to  facilitate 
cleaning. 

Second. — Nitrogen  lamps  placed  at  crossfire  above  the  maze  would  be  better 
than  the  tungstens  surrounding  it,  and  would  do  away  with  the  shadows  caused 
by  the  aluminum  shades,  which,  when  a  very  small  animal  is  the  subject  in  the 
maze,  are  troublesome. 

Third. — A  change  in  the  lighting  arrangement  would  make  it  possible  to  have 
the  mesh  top  made  in  two  pieces  instead  of  four,  and  hinged  to  the  sides  of  the 
maze  so  that  it  could  be  lifted  easily  and  noiselessly,  thus  avoiding  frightening 
the  animal  within  the  maze. 


10 


HELEN  B.  HUBBERT 


accurate  account  of  the  excess  effort  expended,  enabling  a  com- 
parison as  to  the  frequency  and  extent  of  the  several  possible 
errors  as  well  as  a  record  of  the  exact  steps  in  their  elimination. 
It  can  be  determined  whether  a  certain  error  is  lessened  at  each 
trial  and  finally  disappears,  or  whether  it  is  dropped  out  all  at 
once.  In  short  we  have  an  accurate  method  of  tracing  the 
several  factors  involved  in  the  learning  of  the  maze  problem, 
and  a  basis  for  the  analysis  of  the  learning  process  which  has 
heretofore  been  lacking. 


FIGURE  2    Actual  Tracing  of  Pathway  Traversed  by  a  Rat  in  the  Maze 

The  exact  method  employed  in  this  research  concerning  the 
relation  of  age  to  the  learning  ability  was  as  follows: 

One  week  preceding  the  day  on  which  the  animal  was  to 
begin  work,  food  was  removed  from  the  living  cage  and  the  rat 
was  fed  each  day  in  the  center  of  the  maze  which  was  tempor- 
arily partitioned  off  from  the  remainder,  making  it  impossible  for 
him  to  roam  at  will  through  the  maze.  The  first  day,  he  was 
allowed  to  eat  for  forty-five  minutes;  the  second  day,  for  thirty 
minutes;  the  third  day,  for  twenty  minutes.  The  feeding  time 
was  then  diminished  five  minutes  on  each  succeeding  day,  so 


HABIT  FORMATION  IN  THE  ALBINO  RAT  11 

that  the  day  before  beginning  the  problem,  the  rat  had  been 
fed  for  five  minutes  in  the  food  box  of  the  maze.19  Two  things 
were  accomplished  by  this  procedure.  1st:  The  rat  was  ren- 
dered quite  hungry,  a  necessary  step  since  food  was  the  stim- 
ulus used,  but  the  shock  which  would  have  resulted  from  entire 
absence  of  food  was  avoided.  2nd:  It  became  accustomed  to 
some  extent  to  experimental  conditions. 

On  the  day  when  the  problem  was  actually  begun,  the  tem- 
porary partition  was  removed  from  the  maze,  a  dish  of  milk- 
soaked  bread  placed  at  the  center  and  the  rat  put  into  the 
starting  box  (S.  B.  Fig.  1).  The  instant  it  emerged  into  the 
maze  proper,  the  door  (indicated  but  not  shown  in  the  illustra- 
tion), was  closed  behind  it,  making  return  into  the  starting 
box  impossible,  the  stop  watch  was  started  and  the  tracing 
begun.  Twelve  or  fourteen  minutes  might  be  required  to  reach 
the  food,  and  as  many  as  sixteen  sheets  of  paper  have  been 
necessary  to  trace  the  pathway  during  a  single  trial.  At  the 
moment  of  entrance  into  the  food  box  (F.  B.),  the  watch  was 
stopped,  the  time  noted,  and  the  animal  at  once  removed.  This 
constituted  one  trip  or  one  trial.  The  rat  was  immediately 
introduced  for  a  second  trial,  in  which  the  same  procedure  was 
followed  except  that  on  reaching  the  food  it  was  allowed  to  eat 
for  five  minutes  before  being  removed.  The  feeding  period  was 
carefully  timed  with  the  purpose  of  keeping  the  hunger  stimulus 
as  uniform  as  possible.  A  short  ration  of  grain  was  thrown  into 
the  living  cage,  and  no  more  food  was  allowed  until  the  next 
day's  work.  Basset20  had  given  grain  only  twice  a  week,  and 
noted  in  consequence  a  disturbance  in  behavior  on  the  day 
following  that  on  which  grain  was  given.  Ulrich21  fed  his  ani- 
mals in  the  cage  after  work,  which  may  account  for  their  slow- 
ness in  learning  the  maze  as  compared  with  the  rats  used  in  this 
problem. 

Two  trials  were  given  each  day  until  the  problem  was  learned, 
i.  e.,  until  in  six  trips  made  on  three  consecutive  days  no  error 
was  made  from  start  to  finish.  In  both  Basset's  and  Ulrich 's 
work,  a  time  norm  was  set,  and,  although  no  useless  movements 
were  made,  unless  the  act  was  performed  within  the  limits  of 

19  Grain  was  given  in  the  cage  each  day  at  the  end  of  the  feeding  period. 

20  Basset,  G.  C.     Habit  Formation,  etc.     Behavior  Monograph,  2  ('14),  no.  4. 

21  Ulrich.     Behavior  Monographs.     Vol.  II,  No.  5. 


12  HELEN  B.  HUBBERT 

the  time  set,  it  was  not  considered  perfect.  For  the  purposes 
of  this  experiment  such  a  norm  was  not  desirable,  since  one  of 
the  points  under  investigation  was  the  relative  final  rate  of 
efficiency  attainable  by  rats  of  different  ages.  Elimination  of  all 
useless  movements  for  three  days  was  therefore  considered  as 
sufficient  evidence  that  the  problem  had  been  learned.  The 
number  of  trials  required  to  reach  this  level  of  efficiency  varied 
with  each  rat,  the  extreme  limits  being  fourteen  and  one  hun- 
dred twelve  trials.  In  a  single  trial  any  distance  greater  than 
four  and  five  tenths  meters,  which  is  the  length  of  the  errorless 
pathway  from  the  entrance  to  the  food,  represents  excess  effort 
on  the  part  of  the  animal. 

If  a  rat  remained  in  the  maze  for  fifteen  minutes  without 
reaching  the  food  box  he  was  taken  out  and  replaced  in  the 
entrance  box  for  a  second  attempt.  Distance  and  time  were 
recorded  in  the  same  way  as  for  a  successful  run,  i.  e.,  if  the 
first  effort  to  reach  the  food  proved  unavailing  after  fifteen 
minutes,  and  the  second  attempt  was  successful  after  eight 
minutes,  the  total  time  for  the  first  trial  would  be  twenty-three 
minutes  and  the  total  distance  the  combined  distance  of  the  two 
attempts.  Should  the  rat  fail  on  the  second  effort  also,  it  was 
fed  for  three  minutes  in  the  maze  with  the  food  box  partitioned 
off  as  for  preliminary  feeding,  and  tried  again  the  following  day. 

The  time  and  distance  records  for  each  trip  were  carefully 
tabulated,  and  form  the  basis  for  the  conclusions  which  appear 
later.  In  many  cases  the  actual  tracings  were  kept  for  reference. 

EXPERIMENTAL  RESULTS 

It  was  planned  to  work  with  five  groups  of  rats,  twenty-five, 
sixty -five,  two  hundred,  three  hundred  and  five  hundred  days 
old  respectively,  since  it  was  thought  that  these  ages  represented 
fairly  well  the  successive  stages  in  the  growth  and  development 
of  the  animal;  twenty-five  days  for  youth,  sixty-five  days  for 
sexual  maturity,  two  hundred  days  for  maturity,  three  hundred 
days  for  age,  and  five  hundred  days  for  old  age.  The  attempt 
was  made  to  have  thirty  rats  in  each  group,  but  sickness  and 
unavoidable  accidents  among  the  animals  have  brought  the 
number  somewhat  lower.  It  has  been  found  extremely  difficult 
to  obtain  rats  for  the  last  group  (500  days).  Although  Slonaker 
finds  the  average  length  of  life  of  the  white  rat  to  be  thirty-four 


HABIT  FORMATION  IN  THE  ALBINO  RAT  13 

months,22  and  Donaldson  gives  it  as  three  years,  from  three 
hundred  to  four  hundred  days  is  the  maximum  longevity  for 
most  of  the  rats  used  in  this  laboratory,  and  up  to  this  time 
only  twelve  have  lived  to  work  at  the  five  hundred  day  age, 
one  of  these  dying  apparently  of  old  age  before  the  problem  was 
learned.23 

The  groups  used,  with  the  number  of  rats  in  each  group  were 
as  follows: 

Age  at  which  work  began        Number  of  rats  in  the  group 

25  days  27 

65  «  27 

200  "  28 

300  "  28 

500  «  12 

Throughout  the  experiment  two  conditions  have  been  rigidly 
complied  with.  1st:  Every  animal  was  started  on  the  problem 
upon  the  exact  day  at  which  the  proper  age  was  reached.  This 
procedure  was  followed  even  when  it  necessitated  starting 
eighteen  rats  on  the  same  day,  in  order  that  experimental  con- 
ditions might  be  kept  strictly  comparable. 

2nd:  Every  animal  was  run  twice  every  day  from  its  first 
trial  until  the  last,  even  though  at  one  stage  of  the  work  this 
required  having  as  many  as  fifty-eight  rats  under  observation 
at  one  time.  Such  strict  continuity  of  trials  precluded  the 
introduction  of  any  factors  aside  from  those  involved  in  the 
learning  process  proper.  Removal  from  experimental  conditions 
for  even  one  day  would  not  only  cause  a  change  in  the  physiolog- 
ical tonus  of  the  organism,  but  would  also  bring  in  the  matter 
of  retention.  So  far  as  was  possible  the  rats  were  run  at  the 
same  hour  each  day,  but  where  large  numbers  were  being  used, 
it  was  impossible  to  adhere  strictly  to  this  rule,  although  rats 
accustomed  to  run  at  night  did  not  do  so  well  if  used  in  the 
mornings  and  vice  versa;  this  was  probably  attributable  to  the 
acquiring  of  a  certain  food  rhythm  that  might  not  be  broken  with 
impunity.  Thus  it  was  found  that  while  a  difference  of  an  hour 
in  the  working  time,  and  hence  the  feeding  time,  caused  no 

22  Op.  cit.,  Journ.  Animal  Behav.,  pp.  37-38,  tables. 

23  Dr.  Wats9n  has  informed  the  writer  that  his  experience  was  quite  similar, 
very  few  of  his  rats  living  to  be  more  than  500  to  600  days  old. 


14  HELEN  B.  HUBBERT 

noticeable  change  in  the  behavior  of  the  rats,  marked  disturb- 
ance resulted  from  a  delay  of  four  or  five  hours. 

In  general,  the  behavior  of  individuals  of  each  group  on  first 
entering  the  maze  was  the  same.  The  fats  showed  great  hesi- 
tancy in  leaving  the  starting  box,  returned  to  it  frequently 
after  finally  entering  the  maze  proper  and  endeavored  to  push 
up  the  sliding  door;  they  were  slow  to  leave  a  familiar  alley 
for  one  unexplored,  became  excited  when  a  stop  was  encoun- 
tered, trying  repeatedly  to  push  it  aside  or  to  gnaw  through 
the  mesh  top,  and  made  frequent  efforts  to  escape  from  the 
maze.  Departure  from  this  type  of  behavior  was  noticed  among 
the  very  old  rats  and  the  very  young  ones.  Many  of  the  former 
evidenced  no  excitement  whatever,  often  sleeping  for  several 
minutes  between  period  of  activity,  while  the  latter  were  far 
more  active  than  the  rats  of  any  other  group,  and  showed  no 
hesitancy  in  entering  unfamiliar  portions  of  the  maze. 

The  time  usually  decreased  very  rapidly,  the  distance  less 
so,  during  the  first  three  or  four  trials.  For  example,  on  its 
first  trial,  rat  34  of  the  three  hundred  day  group  required  eleven 
minutes  and  forty  seconds  to  reach  the  food,  and  the  distance 
covered  was  forty-nine  and  six  tenths  meters.  On  its  second 
trial,  seven  minutes  six  seconds  were  required,  and  the  distance 
run  was  thirty  and  nine  tenths  meters ;  at  the  fourth  trial,  success 
was  attained  after  one  minute  nineteen  seconds,  the  pathway 
traversed  measuring  ten  and  two  tenths  meters,  while  for  the 
sixth  trial,  the  time  record  was  only  forty-nine  seconds,  the 
distance  eight  and  six  tenths  meters.  By  the  tenth  or  fifteenth 
trial,  the  decrease  in  both  time  and  distance  had  become  much 
more  gradual,  and  continued  so  until  the  problem  was  learned. 
The  rat  referred  to  above,  required  on  the  fifteenth  trial,  twenty- 
four  seconds,  and  ran  seven  and  two  tenths  meters;  on  the 
thirtieth  trial  the  trip  occupied  fourteen  seconds,  and  covered 
five  and  six  tenths  meters.  This  particular  animal  completed 
the  problem  at  the  sixty-sixth  trial,  when  the  time  record  was 
seven  and  two  tenths  seconds,  and  the  distance  record  four  and 
five  tenths  meters,  which,  it  will  be  remembered,  constitutes 
a  perfect  run. 

The  data  set  forth  above  may  be  conveniently  tabulated 
thus: 


HABIT  FORMATION  IN  THE  ALBINO  RAT  15 


Time  required 

Distance  run  in  maze 
before  reaching  food. 

Trial 

to  reach  food          (The  true  pathway  4.5  m.) 

1st 

11  min.  40    sec. 

49.6 

meters 

2nd 

7    "      6      « 

30.9 

u 

4th 

1    "     19      « 

10.2 

u 

6th 

49      « 

8.6 

u 

15th 

24      « 

7.2 

• 

30th 

14      « 

5.6 

u 

66th 

7.2  « 

4.5 

u 

This  rapid  decrease  in  time  and  distance  at  the  beginning 
of  the  problem  was  characteristic  of  all  groups,  and  is  clearly 
shown  in  the  initial  drop  in  all  the  curves. 

TWENTY-FIVE  DAY  RATS 

Work  on  this  group  began  at  twenty-five  days  when  the 
rats  were  so  small  that  they  could  crawl  through  the  mesh  top 
of  the  maze,  and  could  touch  the  sides  of  the  alleys  only  by 
running  from  side  to  side,  while  other  rats  could  remain  in 
the  center  of  the  path  and  touch  both  walls  of  the  runways 
with  their  vibrissae.  These  rats  were  weaned  at  eighteen  days, 
and  were  fed  in  the  maze  for  five  days  preceding  the  experiment, 
the  forty-five  and  thirty  minute  feeding  periods  being  omitted. 
For  the  first  day  or  two  after  starting  the  problem,  they  were 
allowed  to  eat  for  six  or  seven  minutes  instead  of  five  minutes 
at  the  end  of  each  day's  work,  since  it  developed  that  a  shorter 
ration  had  a  weakening  effect  on  animals  so  young.  The  little 
rats  were  exceedingly  active,  and  on  entering  the  maze  ran 
so  rapidly  that  it  was  very  difficult,  but  never  impossible,  to 
trace  their  movements.  For  the  most  part  they  showed  great 
eagerness  to  escape  from  the  starting  box,  some  even  acquiring 
the  habit  of  lifting  the  door  partway  with  the  nose,  and  as  a 
rule  they  had  no  hesitancy  in  entering  unexplored  portions  of 
the  maze,  in  this  respect  differing  from  most  of  the  rats  in  this 
experiment.  The  error  of  circling  the  food  box  occurred  more 
often  with  rats  of  this  group  than  with  those  of  any  other,  the 
explanation  being,  perhaps,  that  in  their  over-eagerness  to  reach 
the  food  they  acquired  such  momentum  than  they  ran  past 
the  entrance  to  the  food  box. 


16 


HELEN  B.  HUBBERT 


Twenty-seven  rats  were  experimented  with  at  this  age,  eleven 
males  and  sixteen  females,  eight  strains  being  represented  as 
follows : 


WM 

1/9/14 

Y(CF) 
2/10/14 

GJ 

3/12/14 

AL 

3/14/14 

XL 

3/15/14 

KL 

9/20/14 

X  W 

11/1/14 

Y  W 

11/1/14 

Total 

Males  .  .  . 
Females. 

All 

0 
2 

2 
1 

1 
1 

1 
1 

1 
3 

3 
5 

1 
3 

2 
0 

11 
16 

2 

3 

2 

2 

4 

8 

4 

2 

27 

The  first  letter  indicates  the  father,  the  second  letter  the 
mother,  of  the  litter.  Individual  rats  were  distinguishable  from 
each  other  by  a  convenient  system  of  ear  marks,  and  on  every 
cage  was  a  tag  showing  the  experimental  number,  parentage, 
date  of  birth,  sex  and  ear  mark  for  each  rat  contained  therein. 
Thus,  W  M  1/9/14  R — 9  4,  would  be  deciphered,  rat  number 
four,  female,  right  ear  straight,  born  January  ninth,  1914, 
mother  M,  father  W. 

The  number  of  trials  required  by  animals  of  this  group  in 
learning  the  problem  varied  from  fourteen  to  fifty-one,  the 
absolute  time  from  four  and  nine-tenths  seconds  to  nine  and 
one-tenth  seconds,  the  total  time  from  sixty-four  minutes  to 
six  hundred  forty-nine  minutes;  and  the  total  distance  from  one 
hundred  thirty-nine  meters  to  four  hundred  eighteen  meters. 

The  "  absolute  time  "  is  the  average  time  for  the  last  six 
trials,  represents  the  limit  of  efficiency  in  speed  for  a  given 
group,  and  varies  among  individual  rats  within  the  group  as 
well  as  for  the  groups  themselves.  Thus,  the  record  time  for 
the  twenty-five  day  group  was  made  by  a  rat  which  could  run 
from  entrance  to  food  box  in  four  seconds,  but  no  other  rat 
attained  this  speed,  and  one  in  particular  could  not  make  the 
run  in  less  than  eight  seconds.  The  last  six  trials  were  all  with- 
out error  and  would  seem  to  afford  a  fair  basis  for  judging  the 
average  final  efficiency,  which  for  this  group  was  five  and  seven- 
tenths  seconds.  The  absolute  distance  is  the  same  for  each 
group,  since  the  last  six  trials  are  errorless,  and  the  true  pathway 
measures  approximately  four  and  five-tenths  meters. 


HABIT  FORMATION  IN  THE  ALBINO  RAT 

TABLE  I 
RUN  IN  DAY  TIME.    RAT  15 — 25  DAYS 

Distance 


17 


Day 

Trial 

Time      Seconds 

Chart 

Maze 

1248.0 
896.0 

678.4 
448.0 

1011.2 
768.0 

460.8 
678.4 

448.0 
768.0 

X  L  3/15/14  B-  male 

4/9/14/ 

2      \ 
4/10    / 

3      \ 
4/11     ) 

4/12     j 

5      \ 

4/3      / 

1 
2 

3 

4 

5 

6 

7 
8 

9 

10 

1'7.8"      67.8 
37.2 

15 
10 

25.8 

17.4 

11.8 
18.6 

10.4 
25.8 

195 
140 

106 
70 

158 
120 

72 
106 

70 
120 

Elim.  4-5-6 
3-4-6-wrong  turn-1 

«     1-3-4-5 
Perfect 

Elim.  l-2-4-5-6-lost  in  3 
«     2-4-5-6-w.  t.  1-3 

«     2-3-4-5-6-W.  t.  1 
"     2-3-4-5-6-W.  t.  1 

Perfect 
Elim.  2-4-5-6-w.  t.  1-3 

6      \ 
4/14     J 

11 
12 

6 
18 

70 
132 

448 
844 

.0 
.8 

Perfect 
Elim.  3-4-5-6-w.  t.  1-2 

7      1 
4/15     ) 

13 
14 

5.6 
6.2 

70 
70 

448 
44 

.0 
.8 

Perfect 

u 

8      \ 
4/16     j 

15 
16 

11. 
32. 

8 

4 

99 
129 

633 

825 

.6 
.6 

Elim.  2-3-4-5-6-ret.  1 
«     2-3-4-5-6-ret.,  w.  1.  1 

9      \ 

4/17     / 

17 
18 

7.8          5. 

7.             7. 

4 
4 

70 
83 

448 
531 

.0 
.6 

Perfect 
Elim.  2-3-4-5-6-W.  t.  1 

10      \ 
4/18    j 

19 
20 

5. 

5. 

4 
2 

70 
70 

448 
448 

.0 
.0 

Perfect 

u 

11      \ 
4/19    / 

21 
22 

5. 
6 

4 

70   ' 
72 

448 
460 

.0 
.8 

u 

Elim.  2-3-4-5-6-too  far  1 

12      1 
4/20    / 

23 

24 

5. 
9 

2 

70 
101 

448 
464 

.0 

.4 

Perfect 
Elim.  2-3-4-5-6-W.  t.  1 

13      \ 

4/21     / 

25 

26 

5 

5. 

6 

70 
70 

448 
'    448 

.0 
.0 

Perfect 

u 

14      \ 
4/22    / 

27 
28 

7. 
5. 

6 

4 

72 
70 

460.8 
448.0 

Elim.  1-2-3-4-6-W.  t.  5 
Perfect 

15      \ 
4/23    / 

16      \ 
4/24    / 

29 
30 

31 
32 

5 
5. 

4. 
4. 

2 

8 

4 

70 
70 

70 
70 

448 
448 

448 
448 

.0 
.0 

.0 
.0 

a 

u 
u 

Finished 
4/25/14 
34  trials 

17      \ 
4/25    / 

33 
34 

4. 
5. 

6 
6 

70 
70 

448 
448 

.0 
.0 

u 
u 

18 


HELEN  B.  HUBBERT 


Rat 


46* 

6 

8 
10 
15 
16 
19 
24 
27 
36 
37 


TABLE  II 

TWENTY-FIVE  DAY  RATS 
11  males — 16  females 


Trials 

18 
45 
32 
28 
34 
27 
40 
24 
51 
30 
30 


Time 
(sees.) 

2541.4 

1903.4 

959.8 

699.6 

423.2 

1592.2 

721.2 

388.4 

1588.0 

1603.2 

1632.8 


Absolute 

Distance          time 
(cm.)  (sees.) 


18035.2 
38666.8 
36732.4 
23770.4 
19424.0 
30016.4 
29207.2 
16131.6 
41816.0 
28454.4 
23070.4 


5.7 
5.1 
5.3 
5.0 
4.9 
5.5 
5.5 
6.1 
5.6 
9.1 
5.5 


19 

2 

5 

9 
11 
12 
13 
14 
17 
20 
21 
22 
25 
28 
31 
41 


Totals 
Averages 

Average  for 
Average  for 


23 
26 
14 
38 
18 
32 
46 
24 
26 
34 
36 
32 
36 
28 
44 
17 


822 
30 

32 
29 


2623.2 

37819.2 

562.2 

21913.6 

3897.2 

30348.8 

723.6 

27129.6 

401.4 

13900.8 

2381.0 

32648.8 

999.4 

30407.0 

519.6 

18553.6 

612.8 

18771.4 

945.6 

25779.2 

900.6 

26208.0 

536.2 

23979.2 

597.6 

30882.8 

2643.2 

36672.0 

1838.2 

30332.2 

2082.8 

23212.8 

36317.8 

733383.8 

1345.1 

27162.3 

1277.5 

27711.3 

1391.5 

26784.9 

7.2 
5.5 
5.2 
5.4 
5.7 
6.1 
4.9 
5.6 
5.6 
5.3 
5.1 
5.4 
5.2 
5.2 
5.2 
7.6 


153.5 
5.7 


5.7 
5.6 


The  enormous  number  of  figures  involved,  makes  the  showing 
of  individual  records  inexpedient.  An  exact  copy  of  the  daily 
record  for  rat  number  fifteen  of  the  twenty-five  day  group, 
from  the  first  to  the  last  trial  appears  as  table  I.  The  averages 
and  totals  for  each  rat  which  appear  in  table  II  are  obtained 
by  adding  and  averaging  the  daily  records  for  the  individual 
rats.  The  total  time,  total  distance,  total  number  of  trials 
and  the  absolute  time  of  the  twenty-seven  rats  were  added  and 
averaged  to  give  the  average  total  time,  the  average  total  dis- 


HABIT  FORMATION  IN  THE  ALBINO  RAT  19 

tance,  the  average  number  of  trials,  and  the  average  absolute 
time  for  the  group. 

The  speed  is  the  average  number  of  centimeters  traveled  per 
second  throughout  the  learning  process,  and  is  obtained  by 
dividing  the  total  time  into  the  total  distance.  For  the  twenty- 
five  day  group  these  averages  were : 

Time 


Trials         Absolute  Total  Distance          Speed 


30  5.7  sec.          224  min.       271.6  meters        20.1 

The  curves  shown  in  fig.  3  are  based  on  the  figures  in  col- 
umns 2,  4  and  6  of  table  II.  Only  one  rat  finished  in  less  than 
fifteen  trials,  and  this  is  indicated  on  the  first  point  of  the  curve. 
Three  rats  finished  at  between  fifteen  and  twenty  trials,  one  at 
seventeen  and  two  at  eighteen  trials  each,  the  average  being 
seventeen  as  indicated  on  the  curve.  Between  twenty  and 
twenty-five  trials  three  rats  finished,  at  twenty-three,  twenty- 
four  and  twenty-four  trials  respectively;  the  average  is  twenty- 
three,  and  the  third  point  on  the  curve  indicates  that  three 
rats  finished  at  twenty-three  trials.  The  same  procedure  is 
followed  in  drawing  the  time  and  distance  curves  except  that 
they  are  necessarily  more  condensed.  Three  rats  required 
approximately  four  hundred  seconds  each  in  which  to  learn 
the  problem,  (numbers  11,  15  and  24),  and  the  first  point  on  the 
time  curve  indicates  this  fact,  The  fourth  point  shows  that 
six  rats  consumed  from  fifteen  thousand  to  twenty  thousand 
seconds  (average  for  the  six,  seventeen  thousand  seconds),  in 
their  total  number  of  trials.  The  fifth  point  in  the  distance 
curve  is  interpreted  to  mean  that  six  rats  covered  between 
three  hundred  thousand  and  three  hundred  fifty  thousand  cen- 
timeters, (average  for  the  six,  one  hundred  seventy  thousand), 
in  learning  the  maze.  It  might  be  well  to  notice  at  this  point 
that  all  of  the  curves  appearing  in  this  paper  are  constructed 
on  this  same  plan. 


20 


HELEN  B.  HUBBERT 


FIGURE  3-A    Trial  Curve  for  Twenty-five  Day  Rats. 

The  trial  curve,  (Fig.  3-A)  for  this  group  reaches  the  apex 
at  about  thirty,  which  is  the  average  number  of  trials  for  this 
age. 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


21 


FIGURE  3-B    Time  Curve  for  Twenty-five  Day  Rats. 

Two  maxima  appear  in  the  time  curve,  (Fig.  3-B)  at 
eight  hundred  seconds,  and  at  seventeen  hundred  seconds  re- 
spectively. A  point  intermediate  between  the  two  would  give 
the  time  average  for  the  group,  approximately  thirteen  hundred 
seconds. 


22 


HELEN  B.  HUBBERT 


FIGURE  3-c    Distance  Curve  for  Twenty-five  Day  Rats. 


The  apex  of  the  distance  curve,  (Fig.  3-C) ,  is  at  three  hundred 
thousand  centimeters,  which  is  not  far  from  the  group  average 
of  two  hundred  seventy  thousand. 

No  very  close  relation  seems  to  obtain  between  the  number 
of  trials  required  for  finishing  the  problem  and  the  total  amount 
of  time  or  distance.  Thus,  the  rat  which  finished  in  fourteen 
trials  had  the  highest  total  time  record  in  the  group,  and  a  high 
distance  record,  while  the  rat  which  finished  in  fifty-one  trials 
had  the  highest  distance  record,  but  a  mean  time  record.  The 
lowest  time  record  was  made  by  a  rat  finishing  in  twenty-four 
trials  whose  distance  record  was  also  low;  the  lowest  distance 
record,  by  a  rat  requiring  eighteen  trials  for  the  problem,  whose 
time  was  lower  than  the  average.  Except  where  the  time 
values  are  very  high,  time  and  distance  bear  a  fairly  constant 


HABIT  FORMATION  IN  THE  ALBINO  RAT  23 

ratio  to  each  other.  The  exceptions  occur  when  the  time  record 
is  increased  on  account  of  failures  (each  of  which  means  a  count 
of  900  seconds)  in  the  first  part  of  the  learning  process.  In  a 
trial  which  has  one  or  more  failures  as  a  component  part,  the 
distance  run  is  never  proportional  to  the  time  spent,  since  if 
the  rat  does  not  refuse  to  run  altogether  after  several  vain 
efforts  to  reach  the  center,  it  will  make  frequent  halts  at  the 
radial  stops  and  at  the  entrance  to  the  maze.  It  appears  that 
we  have  here  additional  evidence  for  considering  the  distance 
as  a  more  accurate  measure  of  the  learning  process  than  the  time. 
According  to  the  averages  which  appear  below,  the  females 
of  this  group  are  superior  to  the  males  in  number  of  trials  re- 
quired to  learn,  and  in  final  efficiency  (absolute  time),  but 
inferior  in  total  time  consumed,  total  distance  covered,  and 
speed  attained  throughout  the  learning  process,  so  that  on  the 
whole,  the  males  may  be  considered  as  slightly  superior  to  the 

females. 

Time 


Trials       Absolute  Total  Distance  Speed 


Males 32  5.7  sec.          213  min.         277.1  m.       21.6  cm.  per  sec. 

Females..  29  5.6    "  232     "  267.8   «       19.2     "      "      " 


SIXTY-FIVE  DAY  RATS24 

These  rats  began  the  problem  when  sixty-five  days  old,  and 
were  fed  in  the  maze  for  one  week  before  actual  experimentation 

24  A  group  of  twenty-seven  thirty-five  day  rats  was  used  early  in  the  experi- 
ment, but  the  results  obtained  from  their  records  were  so  at  variance  with  those 
for  other  groups  that  it  was  felt  there  must  have  been  some  error  in  the  experi- 
mental work.  Accordingly  a  control  group  consisting  of  thirteen  rats  was  trained 
near  the  close  of  the  experiment,  with  no  better  results  so  far  as  consistency  with 
the  main  body  of  averages  of  the  other  groups  was  concerned,  but  with  exactly 
opposite  results  from  those  of  the  first  thirty-five  day  group.  Therefore  neither 
set  of  figures  is  given  in  the  body  of  this  paper,  since  still  further  work  is  neces- 
sary at  that  age  before  any  statements  can  be  made  regarding  it.  The  averages 
obtained  for  the  two  groups  are  given  below: 

Time 


Trials       Absolute  Total  Distance 


First  group 63  6.7  sec.  564  min.         552.2  m. 

Control  group......        22  7.3    «  160     «  156.7   " 


24 


HELEN  B.  HUBBERT 


began.  They  were  lively,  but  did  not  show  the  superabundant 
activity  of  the  twenty-five  day  group,  and  were  not  so  speedy. 
Twenty-seven  rats  were  run,  sixteen  males  and  eleven  females, 
representing  nine  strains  as  follows: 


EJ 

11/1/13 

EL 

11/19/13 

EL 

12/3/13 

WM 

1/8/14 

Y(CF) 
2/10/14 

G  J 

3/12/14 

AL 

3/14/14 

XL 

3/15/14 

Total 

Males.. 
Females 

0 
3 

3 

0 

2 
0 

4 
3 

3 
2 

0 
1 

1 
0 

1 
2 

16 
11 

All  

3 

3 

2 

7 

5 

1 

1 

3 

27 

Trials  varied  from  fourteen  to  sixty-five,  absolute  time  from 
four  and  seven  tenths  to  eleven  and  eight  tenths  seconds,  total 
time  from  sixty-four  minutes  to  seven  hundred  thirty-one  min- 
utes, and  total  distance  from  ninety-one  and  eight  tenths  meters 
to  seven  hundred  fifty  meters.  Here,  as  in  the  preceding  group, 
we  can  trace  no  close  connection  between  number  of  trials  and 
time  or  distance.  The  rat  which  finished  in  the  fewest  number 
of  trials  had  a  low  time  record  and  the  lowest  distance  record 
for  the  group,  while  the  one  requiring  the  greatest  number  of 
trials  had  the  highest  time  and  distance  records.  So  far  the 
relation  seems  very  close.  But  the  lowest  time  record  was 
made  by  a  rat  finishing  in  twenty- two  trials,  whose  distance 
record  was  high,  while  two  other  rats  which  finished  at  twenty- 
two  trials  had  very  high  time  and  distance  records.  The  next 
to  the  highest  distance  record  was  by  a  rat  finishing  in  fifty- 
four  trials,  while  the  next  to  the  highest  time  record  was  made 
by  one  which  finished  in  twenty-two  trials.  In  general,  where 
the  trials  run  very  high  (65,  54)  or  very  low  (14,  16)  the  dis- 
tance corresponds  rather  closely,  but  for  the  trials  lying  between 
these  extremes  no  such  correspondence  can  be  traced.  The 
ratio  between  time  and  distance  in  this  group  is  by  no  means 
constant.  See  table  III.  The  group  averages  are: 


Time 


Trials       Absolute 


Total 


Distance 


Speed 


31 


6.8  sec.          219  min.         260.6  m.       19.8  cm.  per  sec. 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


25 


FIGURE  4-A    Trial  Curve  for  Sixty-five  Day  Rats. 

There  are  two  maxima  in  the  trial  curve  for  this  group,  (Fig. 
4-A),  at  twenty- two  and  thirty-seven  respectively,  and  the 
group  average  lies  midway  between  the  two,  at  thirty-one. 


26 


HELEN  B.  HUBBERT 


FIGURE  4-B    Time  curve  for  Sixty-five  Day  Rats. 


The  time  curve  (Fig.  4-B),  shows  the  highest  point  at  six 
thousand  seconds  and  one  almost  as  high  at  twelve  hundred 
seconds,  while  the  average  number  of  seconds  for  the  group  was 
eleven  hundred. 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


27 


FIGURE  4-c    Distance  Curve  for  Sixty-five  Day  Rats. 

For  the  distance  curve,  (Fig.  4-C),  there  is  a  clearly  marked 
maxima  at  twenty-six,  which  corresponds  exactly  with  the  group 
average  of  twenty-six  hundred  centimeters. 


28 


HELEN  B.  HUBBERT 


TABLE  III 

SIXTY-FIVE  DAY  RATS 
16  males — 11  females 


Absolute 

Time 

Distance 

time 

Rat 

Trials 

(sees.) 

(cm.) 

(sees.) 

26  c? 

14 

454.0 

9184.0 

11.8 

4 

16 

496.0 

11603.2 

9.9 

5 

22 

2378.0 

26675.2 

6.5 

6 

24 

452.4 

18182.4 

6.3 

7 

22 

645.2 

16454.4 

6.6 

8 

30 

385.8 

19718.4 

6.6 

9 

38 

981.4 

25117.6 

7.2 

10 

26 

519.2 

19481.6 

5.6 

11 

18 

1184.8 

18899.2 

5.8 

12 

34 

1724.8 

30498.8 

6.4 

13 

22 

721.0 

16626.4 

5.6 

14 

22 

2700.4 

29484.8 

5.9 

20 

36 

1051.8 

29491.2 

6.9 

21 

46 

1436.4 

33280.0 

5.9 

22 

21 

1344.0 

21305.6 

6.6 

24 

38 

1982.0 

39326.0 

10.6 

19 

30 

1327.4 

23033.6 

8.2 

2 

54 

1651.8 

42368.0 

7.9 

3 

21 

1542.0 

19603.2 

7.1 

15 

28 

2028.0 

28921.6 

5.5 

16 

36 

1139.4 

25177.6 

5.3 

17 

36 

454.4 

20819.2 

4.7 

18 

65 

4388.4 

75001.6 

5.5 

19 

32 

1312.0 

25638.4 

4.9 

23 

38 

815.8 

28409.6 

7.6 

27 

40 

1714.6 

35584.0 

6.4 

28 

20 

597.4 

13849.6 

6.7 

Totals 

830 

35428  4 

703735  2 

184  0 

Averages    

30.7 

1312.1 

26064.2 

6.8 

Average  lord4  ... 

26.8 

1153.6 

22833.0 

7.1 

Average  for  9  ... 

36.5 

1542.8 

30764.2 

6.3 

Comparison  of  the  male  and  female  records  in  the  group 
show  that  while  the  absolute  time  of  the  females  is  less  than 
that  of  the  males,  in  other  respects  the  male  showing  is  the 
better. 


Time 


Trials       Absolute 


Males... 
Females. 


27 
36 


7.1  sec. 
6.3    « 


Total 

192  min. 
257     " 


Distance 

228.3  m. 
307.6   « 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


29 


Two  HUNDRED  DAY  RATS 

These  rats  were  put  to  work  when  two-hundred  days  old, 
having  been  fed  in  the  maze  for  one  week  preceding  the  begin- 
ning of  the  problem.  They  were  more  erratic  than  those  of  any 
other  group  used,  being  jerky  and  irregular  in  their  movements. 
Often  after  making  a  perfect  run  in  six  or  seven  seconds  a  rat 
would  drop  back  to  one,  two  or  three  minutes  with  many  errors! 
This  behavior  was  not  noted  in  any  other  group  except  in  one 
or  two  isolated  cases. 

Twenty-eight  rats  were  used,  fifteen  males  and  thirteen  fe- 
males, eight  families  being  represented  as  follows: 


BD 

7/26/13 

CC2 

7/30/13 

WG 

8/24/13 

BD 

8/28/13 

BH 

9/18/13 

BH 

9/25/13 

WK 

10/2/13 

XL 

3/15/14 

Total 

Males.. 
Females 

All  

1 
0 

1 
2 

3 
2 

1 
2 

2 

4 

3 
2 

2 
0 

2 
1 

15 
13 

1 

3 

5 

3 

6 

5 

2 

3 

28 

Trials  varied  in  number  from  fourteen  to  one  hundred  twelve, 
absolute  time  varied  from  five  and  two  tenths  seconds  to  twenty- 
four  and  one  tenth  seconds,  total  time  from  eighty-two  to  nine- 
hundred  forty-nine  minutes,  and  total  distance  from  one-hundred 
twenty-five  and  five  tenths  meters  to  nine-hundred  and  twelve 
meters.  As  for  previous  groups,  trials  bear  little  relation  to 
time  or  distance,  but  the  proportion  between  total  time  and 
total  distance  is  fairly  constant.  (See  Table  IV).  The  lowest 


30 


HELEN  B.  HUBBERT 


TABLE  IV 

Two  HUNDRED  DAY  RATS 
15  males — 13  females 


Rat 


2C? 
5 

8 

9 
10 
11 
23 
24 
29 
30 
31 
33 
34 
36 
38 

39 

4 

6 

7 
15 
17 
18 
19 
20 
21 
25 
27 
35 


Totals... 
Averages. 


Average 
Average  for  Q 


Trials 

81 

28 

44 

26 

20 

20 

30 

30 
104 
107 

64 

32 

22 

32 

14 

26 
112 
18 
54 
32 
56 
79 
49 
27 
32 
35 
22 
37 

1170 
41.7 

39.4 

44.5 


Time 

(sees.) 


810.2 

1548.2 

1767.0 

646.3 

496.4 

1548.6 

1191.0 

1564.8 

2636.1 

4735.6 

1877.2 

1343.8 

1084.6 

777. 8 

732.8 

1280.4 
3014.0 
1825.2 
3851.1 
2409.0 
2995.8 
3663.4 
2031.4 
5694.8 
2440.0 
2990.6 
963.4 
3135.8 

36294.9 
2109.1 

1517.3 
2791.9 


Distance 
(cm.) 

51010.4 
21932.4 
30275.2 
16672.0 
12559.2 
18387.2 
22828.8 
28355.2 
64632.2 
91293.8 
47627.2 
25446.4 
18240.3 
18675.2 
12569.6 

19744.0 
69781.6 
13475.2 
51143.4 
31522.8 
46335.8 
59373.2 
44944.4 
32960.0 
35686.0 
35897.6 
19043.6 
45104.8 

949517.5 
33911.1 

29633.6 
38847. 1 


Absolute 
time 

(sees.) 

8.7 

8.6 
10.7 

5.7 

6.8 

7.4 

7.0 

7.6 
17.3 
24.1 

6.5 

8.5 


10.5 
8.1 
7.9 

9.4 
7.4 
8.0 
7.2 
5.2 
6.5 
6.6 
5.4 
8.7 
6.1 
7.8 
7.8 
7.3 


238.8 
8.5 

9.7 
7.2 


trial  record  was  fourteen,  and  the  time  and  distance  records 
for  the  rat  making  this  record  were  also  low.  The  lowest  time 
record,  as  well  as  the  lowest  distance  record  was  made  by  a  rat 
finishing  in  twenty  trials.  The  rat  requiring  the  largest  number 
of  trials  (112)  had  a  time  record  but  little  higher  than  one  which 
required  only  thirty-four  trials,  while  its  distance  record  was 
next  to  the  highest.  The  highest  time  record  was  that  of  a 
rat  which  finished  in  one  hundred  seven  trials,  with  the  next 
to  the  highest  distance  record,  the  highest  distance  record  by 
one  finishing  in  twenty-seven  trials,  whose  time  was  consid- 
erably above  the  average. 


HABIT  FORMATION  IN  THE  ALBINO  RAT 
The  averages  for  this  group  are: 

Time 
Trials       Absolute  Total  Distance  Speed 


31 


42 


8.6  sees.         351  min.         339.1  m.       16  cm.  per  sec. 


FIGURE  5-A    Trial  Curve  for  Two  Hundred  Day  Rats 

The  apex  of  the  trial  curve,  Fig.  5-A,  lies  at  thirty-three, 
while  the  average  for  the  group  is  forty-one,  but  the  explanation 
of  the  apparent  discrepancy  is  to  be  found  in  the  records  of 
the  six  rats  who  required  from  fifty-six  to  one  hundred  twelve 
trials  to  learn  the  problem,  thus  running  the  group  average  up. 
No  well  defined  apex  can  be  found  in  the  time  curve  (Fig.  5-B), 
the  group  average,  twenty-one  hundred  seconds  showing  rather 
as  a  depression,  nor  could  it  be  divined  by  a  glance  at  the  dis- 
tance curve  (Fig.  5-C)  that  the  average  lay  in  the  neighborhood 
of  thirty-three  thousand  centimeters. 


32 


HELEN  B.  HUBBERT 


FIGURE  SB    Time  Curve  for  Two  Hundred  Day  Rats 


HABIT  FORMATION'  IN  THE  ALBINO  RAT 


33 


FIGURE  5-c    Distance  Curve  for  Two  Hundred  Day  Rats. 

If  the  averages  for  the  males  and  females  be  compared,  it 
appears  that  the  former  are  somewhat  superior  to  the  latter 
except  in  absolute  time.  The  averages  are: 


Time 


Trials       Absolute 


Total 


Males. .. 
Females. 


39 
45 


9.7  sec. 
7.2    « 


219  min. 
465     « 


Distance 

296.3  m. 

388.4  " 


THREE  HUNDRED  DAY  RATS 

This  group  consisted  of  twenty-eight  rats  from  ten  families, 
thirteen  males  and  fifteen  females,  who  began  the  problem  when 
three  hundred  days  old. 


34 


HELEN  B.  HUBBERT 


<NJ 

<N 

CM 

CM 

CM 

CM 

n^ 

fe  \ 

fe  rH 

fc  ^H 

fe  \ 

W  \ 

fe  ~^- 

AD 

w 

£2 

^CM 

WCM 

^CO 

W^ 

°\ 

pg2 

U^ 

Total 

W 

LO 

LO 

to 

to 

to 

to 

to 

Males  

0 

1 

0 

1 

0 

4 

1 

2 

2 

2 

13 

Females  

1 

4 

1 

1 

2 

2 

2 

1 

1 

0 

15 

All  

1 

5 

1 

2 

2 

6 

3 

3 

3 

2 

28 

They  were  fed  in  the  maze  for  ten  days  before  the  beginning 
of  the  problem,  preliminary  feeding  being  thus  extended  because 
it  was  found  that  rats  so  old  contracted  digestive  troubles  unless 
the  decrease  in  food  supply  was  made  more  gradual  than  for 
the  younger  animals.  They  were  allowed  to  eat  for  from  six 
to  eight  minutes  instead  of  five,  at  the  close  of  each. day's  work, 
since  they  ate  much  slower  than  the  younger  rats,  and  could 
not  obtain  sufficient  nourishment  in  the  shorter  time.  These 
rats  differed  markedly  in  behavior  from  those  in  any  of  the 
preceding  groups  in  that  they  were  lethargic,  inactive,  and  often 
went  to  sleep  in  the  maze  instead  of  working  at  their  problem. 
A  few  of  the  animals  of  this  group  were  from  The  Wistar  Insti- 
tute, and  were  somewhat  timid  and  difficult  to  handle,  but  even 
among  animals  bred  in  this  laboratory  the  same  disinclination 
to  work  was  noted,  although  with  our  own  rats  it  did  not  last 
so  long.  When  the  rats  finally  began  to  work,  they  went  about 
it  differently  from  those  of  other  groups.  They  were  very  de- 
liberate, followed  the  culs  de  sac  out  to  the  bitter  end  whereas 
the  other  rats  often  turned  back  toward  the  true  path  before 
reaching  the  alley  stop;  furthermore,  they  did  not  hesitate  to 
enter  the  unexplored  runways  as  did  most  of  the  other  rats, 
in  this  last  respect  resembling  the  twenty-five  day  rats. 

The  trials  varied  from  fourteen  to  eighty-four,  absolute  time 
from  five  and  eight  tenths  seconds  to  thirty-five  and  two  tenths 
seconds,  total  time  from  one  hundred  nine  minutes  to  two 
thousand  two  hundred  seventy-four  minutes,  and  total  distance 
from  one  hundred  seventeen  and  three  tenths  meters  to  six 
hundred  nine  and  six  tenths  meters. 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


35 


Rat 


22 
24 
25 
26 
30 
33 
34 
36 
37 
38 
39 


TABLE  V 

THREE  HUNDRED  DAY  RATS 
13  males — 15  females 


Trials 

29 
48 
82 
42 
54 
19 
27 
16 
66 
26 
44 
34 
35 


Time 


8221.0 
1943.8 
1222.06 
5605.8 
1862.4 
8937.2 
3167.4 
956.4 
2899.0 
2618.4 
2861.2 
1706.6 
4227.2 


Distance 
(cm.) 

30962.8 
35558.4 
72300.4 
43411.2 
33017.6 
33760.0 
19980.8 
11731.2 
55929.6 
24358.4 
33068.8 
28793.6 
35916.8 


Absolute 
time 
(sees.) 

12.7 

9.5 
14.5 
13. 
10. 
11 
13. 
19. 
10.7 

8.6 
13.0 

6.5 

6.9 


19 

2 

9 
12 
14 
15 
16 
18 
19 
20 
21 
27 
28 
31 
35 


Totals. . . 
Averages. 


Average 
Average  for  9 


20 

11113.2 

62 

4745.6 

25 

7029.6 

24 

13639.6 

19 

4320.6 

78 

2646.4 

20 

1640.2 

40 

2431.4 

14 

1598.4 

58 

4614.9 

30 

1682.6 

70 

7567.6 

38 

1134.0 

84 

2087.0 

38 

1438.4 

1142 

124916.5 

40.7 

4461.3 

40.4 

4402.0 

41.3 

4512.6 

31609.6 
56636.4 
34898.6 
32563.0 
26163.2 
50601.8 
18227.2 
42406.4 
15059.2 
66342.4 
26035.2 
60960.0 
24652.8 
56115.2 
28076.8 

1029137.4 
36754.9 

34437.6 
38023.1 


35.2 

5.8 

9.0 

7.4 

21.4 

11.5 

14.3 

6.6 

13.0 

15.5 

8.3 

6.2 

6.2 

8.3 

6.7 


325.4 
11.6 

11.5 
11.7 


No  connection  between  number  of  trials  and  time  or  distance 
was  found,  and  the  ratio  of  total  time  to  total  distance  did 
not  appear  to  be  constant.  (Table  V).  Thus,  the  lowest  num- 
ber of  trials  (14)  was  made  by  a  rat  whose  total  distance  was 
next  to  the  lowest,  but  whose  time  record  was  higher  than  that 
of  one  rat  finishing  at  sixteen  trials  and  those  of  two  rats  finish- 
ing at  thirty-eight  trials  each.  The  greatest  number  of  trials 
(84)  was  made  by  a  rat  whose  time  record  was  exceeded  by 
eighteen  others,  while  its  distance  record  was  exceeded  by  four 


36 


HELEN  B.  HUBBERT 


others.  The  lowest  time  record  as  well  as  the  lowest  distance 
record  was  made  by  a  rat  which  finished  in  sixteen  trials,  the 
highest  time  record  by  one  requiring  twenty-four  trials,  whose 
distance  record  was  an  average  one.  The  highest  distance  record 
belongs  to  the  rat  with  next  to  the  highest  number  of  trials 
whose  time  is  also  next  to  the  greatest. 
Group  averages  were: 


Time 


Trials 
41 


Absolute 


Total 


Distance 


Speed 


11.6  sec.         743  min.         367.5  m.       8.2  cm.  per  sec. 


FIGURE  6-A    Trial  Curve  for  Three  Hundred  Day  Rats 

The  apex  of  the  time  curve  (Fig.  6-A)  lies  at  twenty-eight, 
although  the  average  is  forty-one.  The  large  number  of  rats 
finishing  after  thirty  trials  however  easily  accounts  for  the 
apparent  discrepancy.  Two  maxima  are  found  in  the  time 
curve,  (Fig.  6-B),  at  seventeen  hundred  and  twenty-eight  hun- 
dred respectively,  but  again  the  general  average  is  raised  by  the 
twelve  animals  who  required  more  than  three  thousand  seconds 
in  which  to  learn  the  maze  pathway.  There  is  a  decided  apex 
in  the  distance  curve  (Fig.  6-C)  at  thirty-three  thousand,  which 
nearly  corresponds  with  the  group  average  of  thirty-six  thousand. 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


37 


I 


38 


HELEN  B.  HUBBERT 


FIGURE  6-c    Distance  Curve  for  Three  Hundred  Day  Rats 

There  was  almost  no  difference  between  the  learning  of  the 
males  and  that  of  the  females,  such  difference  being  even  less 
marked  than  in  the  twenty-five  day  group.  The  averages  are: 


Time 


Trials       Absolute 


Total 


Males... 
Females. 


40 
41 


11.5  sec. 
11.7    " 


733  min. 
752     « 


Distance 

344.8  m. 
380.2  « 


FIVE  HUNDRED  DAY  RATS 

Records  on  only  eleven  rats  have  been  obtained  in  this  group, 
six  strains  being  represented  by  four  males  and  seven  females 
who  began  the  problem  when  five  hundred  days  old.  These 
rats  like  the  300-day  animals,  were  fed  in  the  maze  for  ten  days 
previous  to  the  commencement  of  the  problem,  and  allowed  to 
eat  for  from  six  to  eight  minutes  at  the  close  of  each  day's  work 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


39 


on  account  of  their  age.     Little  difference  in  behavior  was  noted 
between  them  and  the  three  hundred  day  animals. 


CF 

6/12/1 

BE 

6/18/13 

CF 

6/21/13 

BH 

9/25/13 

WK 
10/7/13 

EJ 

11/11/13 

Total 

Males  .    .  . 

0 

0 

1 

0 

3 

0 

4 

Females.  .  . 

1 

1 

2 

1 

0 

2 

7 

All 

1 

1 

3 

1 

3 

1 

11 

Too  few  rats  have  been  used  to  make  this  group  really  com- 
parable with  the  rest,  but  averages  and  totals  are  nevertheless 
shown.  Trials  varied  in  number  from  eighteen  to  fifty-six,  ab- 
solute time  from  five  and  four  tenths  seconds  to  seventeen  and 
eight  tenths  seconds,  total  time  from. one  hundred  and  sixty- 
seven  minutes  to  eleven  hundred  and  sixty-seven  minutes,  and 
total  distance  from  one  hundred  seventy-two  and  eight  tenths 
meters  to  six  hundred  forty-one  and  six  tenths  meters. 

Again  there  is  no  relation  apparent  between  trials  and  time 
or  distance,  and  total  time  and  total  distance  do  not  bear  a 
proportional  relation  to  each  other.  (Table  VI).  The  rat  which 

TABLE  VI 
FIVE  HUNDRED  DAY  RATS 

4  males — 7  females 


Rat 


9 
10 
11 


Trials 

32 
43 
18 
56 


Time 

(sees.) 


1331.8 
7004.0 
6021.8 
2877.6 


Distance 
(cm.) 

20922.2 
42167.8 
17280.0 
64167.4 


Absolute 
time 
(sees.) 

16.2 

7.6 

17.8 

5.4 


1$ 

2 
3 

4 
7 
12 
'        14 

47 
34 
45 
38 
32 
38 
30 

3117.3 
1570.2 
3763.8 
3124.2 
1005.2 
3534.0 
3443.0 

41450.4 
27381.6 
37791.2 
30559.6 
20577.0 
46364.4 
30616.8 

13.2 
9.4 
10.5 
7.5 
8.7 
9.9 
11.7 

Totals  

413 

36792  9 

379278  4 

117  9 

Averages  

38 

3344  9 

34479  9 

10  7 

Average  ford"'  .  .  . 
Average  for  $  ... 

38 
37 

4326.3 
2794.0 

36134.3 
33534.4 

11.8 
10.1 

40 


HELEN  B.  HUBBERT 


finished  in  the  fewest  trials  (18)  had  next  to  the  highest  time 
record  but  the  lowest  distance  record,  while  the  rat  requiring 
the  greatest  number  of  trials  (56)  had  a  time  record  lower  than 
the  average,  with  the  highest  distance  record.  The  highest 
time  record  was  made  by  a  rat  which  finished  in  forty-three 
trials,  whose  distance  record  was  excelled  by  one  other,  the 
lowest,  by  one  which  finished  in  thirty-two  trials  with  a  dis- 
tance record  next  to  the  lowest. 
Group  averages  are: 


Time 


Trials       Absolute 


Total 


Distance 


Speed 


38 


10.7  sec.         557  min.         332.9  m.       9.9  cm.  per  sec. 


Discussion  of  the  curves  seems  hardly  worth  while  in  view 
of  the  small  number  of  results  on  which  they  are  based.  The 
average  number  of  trials  lies  between  the  two  apices  of  the 
trial  curve,  (Fig.  7-A),  the  average  amount  of  total  time  re- 
quired, thirty- three  hundred  seconds,  agrees  with  the  second 
maximum  in  the  time  curve,  (Fig.  7-B),  and  the  distance  aver- 
age lies  at  the  middle  one  of  the  three  maxima  of  the  distance 
curve.  (Fig.  7-C). 


FIGURE  7-A    Trial  Curve  for  Five  Hundred  Day  Rats 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


41 


FIGURE  7-B    Time  Curve  for  F'ive  Hundred  Day  Rats 


00 


tt 


CTC 


FIGURE  7-c    Distance  Curve  for  Five  Hundred  Day  Rats 


42 


HELEN  B.  HUBBERT 


The  males  appear  to  be  inferior  to  the  females  as  is  shown 
by  comparing  the  averages  for  the  two  sexes: 

Time 


Trials25      Absolute 


Total 


Males... 
Females. 


38 
37 


11.8  sec. 
10.1    " 


721  min. 
466     « 


Distance 

361.3  m. 
313.9  « 


COMPARISON  OF  RESULTS  OBTAINED  FOR  THE 
DIFFERENT  AGES 

TABLE  VII 
GENERAL  AVERAGES 
Time 


Age 

25  days: 
Males  . . 
Females 
All  .. 


Trials      Absolute 


65  days: 
Males  . . 
Females 
All  .. 


200  days: 
Males  . . 
Females 
All.. 


300  days: 
Males  . . 
Females 
All.. 


32 
29 
30 

27 
37 
31 

39 

45 
42 


40 
41 
41 


5. 7  sec. 

5.6  « 

5.7  « 


7.1 
6.3 
6.8 

9.7 

7.2 
8.6 


11.5 
11.7 
11.6 


Total 


213  min. 
232     « 
224     « 


192 
257 
219 


263 
465 
351 


734 
752 
743 


Distance 


277.6m. 
267.8  « 
271.6  « 


228.3  « 

307.6  « 

260.6  « 

296.3  « 

388.4  « 

339.1  « 

344.3  « 

380.2  « 

367.5  « 


Speed 


21 . 6  cm.  per  second 

1  C\    O  W  U  ft 

lC7  .  ^ 

20.1  "  «        « 

19.8  «  ' 

19.9  «  ' 
19.8  "  ' 

19.5  «  * 

13.8  «  ' 

16.0  «  ' 

7.8  «  ( 

8.2  «  ' 

8.2  "  ' 


Table  VII  shows  the  general  averages  for  each  age  as  well 
as  those  for  the  males  and  females  separately.  Averages  for 
the  five  hundred  day  rats  are  omitted  for  reasons  already  given. 

25  Two  five  hundred  day  rats  did  not  finish  the  problem.  Each  had  been  given 
sixty  trials  when  the  experiment  had  to  be  discontinued.  The  records  were: — 

Total  time      Total  distance 

Rat  no.  15 13046.2  sec.        58371.2  m. 

«      "    16 17400.2    «          64174.4" 

Rat  number  15  had  made  five  perfect  runs  in  the  course  of  his  training,  but  had 
never  gone  perfect  twice  in  succession. 

Rat  number  16  had  made  twelve  perfect  runs,  and  on  two  occasions  had  trav- 
ersed the  path  twice  in  succession  without  error,  but  never  succeeded  in  doing  it 
three  times  in  succession. 

The  time  record  for  each  rat  is  greatly  above  that  of  any  rat  shown  in  table  VI. 
The  distance  record  of  rat  16  is  slightly  above  the  maximum  for  the  five  hundred 
day  rats  as  recorded  in  the  table,  and  that  9f  rat  15  nearly  reaches  it.  Had  it 
been  possible  to  continue  the  experiment  until  both  of  these  animals  learned  the 
problem,  the  group  averages  for  the  five  hundred  day  rats  would  have  been  con- 
siderably increased. 


HABIT  FORMATION  IN  THE  ALBINO  RAT  43 

The  number  of  trials  required  by  the  rats  in  order  to  learn 
the  maze  increases  with  age  except  in  the  case  of  the  three 
hundred  day  group  where  the  average  is  very  slightly  below 
that  of  the  two  hundred  day  group. 

The  sixty-five  day  males  learned  the  problem  in  fewer  trials 
than  the  twenty-five  day  ones  but  the  females  of  the  older  group 
required  more  trials  than  those  of  the  younger.  There  is  rather 
a  sharp  dividing  line  between  the  young  animals  (25  and  65 
days)  and  the  old  animals  (200  and  300-days)  the  former  ac- 
quiring the  maze  habit  with  considerably  fewer  trials  than  the 
latter. 

The  total  time  consumed  in  perfecting  the  habit  also  shows 
a  regular  increase  with  age  except  for  the  sixty-five  day  rats 
whose  time  record  is  slightly  below  that  of  the  twenty-five  day 
ones.  The  apparent  superiority  of  the  older  group  over  the 
younger  is  attributable  solely  to  the  record  made  by  the  males, 
since  the  females  at  sixty-five  days  have  a  higher  record  than 
those  at  twenty-five  days.  Again  we  see  that  the  two  younger 
groups  are  quite  distinct  from  the  two  older  ones,  requiring 
considerably  less  total  time  in  which  to  learn  the  problem. 
The  high  average  of  the  three  hundred  day  group  is  due  in  part 
to  the  large  number  of  failures  which  occurred  in  early  trials 
at  that  age,  but  is  also  partly  attributable  to  their  slower  bodily 
movements. 

Total  distance  shows  a  regular  increase  with  increasing  age 
except  for  the  sixty-five  day  group,  where  again  the  lowering 
of  the  average  is  due  to  the  superiority  of  males  over  those  of 
the  twenty-five  day  group,  the  females  being  superior  in  the 
twenty-five  day  group  as  compared  with  the  sixty-five  day 
group.  The  difference  between  the  «two  younger  groups  and 
the  two  older  ones  is  not  so  marked  as  that  for  trials  or  time, 
but  it  is  nevertheless  apparent  that  the  members  of  the  latter 
covered  more  ground  than  those  of  the  former.  Yerkes  found 
his  older  dancers  somewhat  superior  to  the  younger  ones  in 
learning  the  labyrinth.  The  writer  finds  that  the  younger 'rats 
learn  the  maze  in  fewer  trials,  that  their  absolute  time  is  less, 
their  total  time  and  distance  are  less,  and  that  their  speed  is 
greater  than  in  the  case  of  the  older  rats.  His  ten  month  dan- 
cers were  superior  to  those  of  one  to  two  months  while  the 
twenty-five  and  sixty-five  day  rats  of  this  experiment  form 


44  HELEN  B.  HUBBERT 

the  maze  habit  more  quickly  than  those  three  hundred 
days  old. 

The  speed  (which  it  will  be  remembered  is  the  average  num- 
ber of  centimeters  run  per  second  throughout  the  learning  pro- 
cess, no  distinction  being  made  between  early  and  late  trials) 
without  exception  decreases  with  increased  age.  The  last  group 
is  distinctly  slower  than  any  other  and  this  to  our  mind  is  again 
proof  of  the  lessening  of  activity  with  age. 

The  absolute  time,  which  we  have  taken  as  the  indication 
of  final  efficiency,  also  diminished  with  increasing  age,  and  is 
considerably  lower  at  three  hundred  days  than  at  any  previous 
age.  Thus,  while  at  twenty-five  days  the  average  length  of 
time  required  for  the  execution  of  a  perfect  run  was  five  and 
seven  tenths  seconds,  at  three  hundred  days  the  very  best  time 
in  which  the  food  could  be-  reached  was  eleven  and  six  tenths 
seconds,  more  than  twice  the  time  of  the  youngest  group.  It 
follows  -that  in  the  formation  of  habits  in  which  the  factor  of 
speed  is  of  an  importance,  equal  to  or  greater  than  that  of  ex- 
actness, the  older  animals  would  be  considerably  handicapped. 
In  the  field  of  animal  experimentation  illustrations  of  habits 
where  speed  is  an  important  factor  are  difficult  to  find.  On 
the  human  side  such  an  illustration  might  be  had  in  the  ac- 
quiring of  technique  in  piano  playing  or  voice  culture,  either 
of  which  demands  the  rapid  succession  of  the  muscular  activ- 
ities involved  in  rendering  scales,  arpeggios,  trills,  etc.  It  would 
seem  that  habits  requiring  extreme  rapidity  of  execution  within 
a  prescribed  rhythm  could  not  be  learned  by  the  older  animals. 

A  comparison  of  the  relation  of  distance  to  time  in  the  younger 
and  older  groups  is  interesting.  In  the  first  two  groups  the 
distance  is  relatively  high*  showing  the  excess  activity  displayed 
by  the  younger  animals,  in  the  two  hundred  day  group  it  is 
about  the  same  as  the  time,  indicating  that  excess  activity  is 
at  a  minimum,  while  in  the  last  group  it  is  much  less  than  the 
time,  showing  that  the  effects  of  old  age  have  begun  to  manifest 
themselves  through  a  general  slowing  up  of  activity. 

If  the  distance  alone  be  taken  as  a  measure  of  activity,  our 
results  agree  with  those  of  Slonaker  who  found  the  most  active 
age  to  be  between  ten  and  twelve  and  a  half  months,  since  our 
three  hundred  day  rats  covered  more  distance  in  learning  the 
problem  than  any  other  group.  If,  however,  distance  be  con- 


HABIT  FORMATION  IN  THE  ALBINO  RAT  45 

sidered  in  relation  to  time,  the  older  rats  appear  much  less  active 
than  the  younger  ones,  as  is  shown  by  the  average  high  speed 
attained  by  the  young  in  comparison  with  the  old.  Certainly 
the  behavior  of  the  old  animals  when  in  the  maze  is  much  more 
deliberate  than  that  of  the  young  ones,  and  the  writer  believes 
that  if  Slonaker  had  possessed  some  means  of  measuring  the 
amount  of  activity  per  unit  of  time  he  would  have  found  the 
young  far  more  active  than  the  old. 

In  Table  VIII  is  given  the  average  speed  for  each  group, 
for  the  first,  second  and  tenth  trials,  the  two  trials  immediately 
preceding  the  last  six,  and  the  last  six  trials.  The  increase 
of  speed  from  the  first  to  the  second  trial  is  considerable  except 
in  the  two  hundred  day  group  where  there  is  a  decided  decrease. 
The  gain  from  the  second  to  the  tenth  trial  is  great  except  for 
the  three  hundred  day  group  where  it  is  comparatively  small. 
From  the  tenth  trial  to  the  two  preceding  the  last  six  the  gain 
for  the  two  hundred  and  three  hundred  day  groups  is  greater 
than  for  the  twenty-five  or  sixty-five  day  groups,  and  from 
these  two  trials  to  the  last  six  trials  the  gain  is  again  greater 
for  the  three  hundred  day  rats.  This  gives  a  slight  indication 
as  to  where  the  most  rapid  learning  occurs.  A  full  set  of  tables 
showing  the  speed  for  every  trial  of  each  group  would  be  neces- 
sary for  an  adequate  discussion  of  the  question,  but  from  the 
present  incomplete  data  it  appears  that  the  learning  in  the 
two  younger  groups  is  most  rapid  during  the  early  stages,  while 
for  the  older  groups  it  is  more  rapid  during  the  later  trials. 
Especially  is  this  true  of  the  three  hundred  day  group,  the 
increase  in  speed  being  very  gradual  during  the  first  ten  trials 
then  more  than  doubling  from  the  tenth  to  the  two  immediately 
preceding  the  last  six.  In  general,  speed,  for  the  separate  trials 
tabulated,  decreased  with  age,  which  accords  with  our  obser- 
vation on  the  average  speed  for  each  group  during  the  entire 
period  of  formation  of  the  maze  habit. 

TABLE  VIII 
SPEED — CENTIMETERS  PER  SECOND 

Two 

First         Second        Tenth      preceding        Last 
Age  trial  trial  trial          last  six  six 

25  days  7.8  9.8  52.0  74.2  90.0 

65      "  7.2  11.1  35.0  52.0  75.0 

200    "  8.3  4.7  21.0  40.7  56.2 

300      «  3.0  4.2  9.5  20.8  40.9 


46 


HELEN  B.  HUBBERT 


INCIDENTAL  TESTS 

Although  the  primary  object  of  this  investigation  was  to 
determine  the  relation  of  age  to  rapidity  of  habit  formation, 
several  minor  points  of  interest  have  been  touched  upon  in  the 
course  of  the  experimentation  which  it  may  be  well  to  mention. 

EFFECT  OF  SEX  ON  RAPIDITY  OF  LEARNING 

The  ideal  way  in  which  to  test  this  matter  would  be  to  have 
an  equal  number  of  males  and  females  from  each  litter  used, 
and  at  least  twenty  animals  of  each  sex  used  at  each  age.  In 
our  work  this  was  impossible,  but  the  averages  given  in  Table 
IX  are  in  no  instance  based  on  less  than  eleven  animals,  the 
number  in  each  case  being  given. 


Age 


25  days: 
11  Males... 
16  Females. 

65  days: 
16  Males... 
11  Females. 

200  days: 
15  Males... 
13  Females. 

300  days: 
13  Males... 
15  Females. 

Gen.  Av.: 
55  Males... 
55  Females. 


TABLE 

Time 

IX 

Trials 

Absolute 

Total 

32 
29 

5.7  sec. 
5.6    « 

213 
232 

min. 

« 

27 
37 

7.1     « 
6.3     « 

192 
257 

u 
u 

39 

45 

9.7    " 
7.2     " 

263 
465 

u 
u 

40 
41 

11.5     « 
11.7     " 

734 
752 

u 
u 

35 
38 

8.2     « 

7.7    « 

351 

427 

u 
u 

Distance 


277.1  m. 
267.8   « 


228.3   " 
307.6   " 


296.3 
388.4 


344.3 
380.2 


286.5   « 
336.0   " 


Speed 


21 . 6  cm.  per  sec. 
19.2    "      "      " 


19.8 
19.9 


19.5 
13.8 


7.8 
8.2 


17.2 
15.3 


It  may  be  seen  from  the  table  that  the  males  are  at  every 
age  somewhat  superior  to  the  females  in  learning  ability,  their 
superiority  being  less  marked  in  the  young  and  old  groups  (25 
and  300  days)  than  in  the  two  intermediate  groups  (65  and  200 
days).  The  general  averages  for  an  equal  number  of  males  and 
females  show  the  males  superior  to  the  females  in  all  points 
save  one,  that  of  absolute  time.  They  finished  in  fewer  trials, 
required  less  total  time,  and  covered  a  smaller  amount  of  dis- 


HABIT  FORMATION  IN  THE  ALBINO  RAT  47 

tance  in  learning  the  problem  than  did  the  females,  while  their 
speed  was  slightly  higher.  This  conclusion  is  at  variance  with 
that  of  Yerkes  regarding  the  dancer,  he  having  found  the  females 
superior  to  the  males  in  learning  the  labyrinth.  In  the  matter 
of  final  efficiency  as  evinced  by  the  absolute  time,  the  females 
are  superior  to  the  males  at  all  ages  except  three  hundred  days 
when  the  two  records  are  practically  equal.  The  general  aver- 
age shows  this  to  be  the  one  point  wherein  the  record  for  the 
females  is  better  than  that  for  the  males. 

The  mean  variation  from  the  time  average  is  less  for  the 
males  at  all  ages,  their  distance  variation  is  less  at  sixty-five 
and  three  hundred  days.  The  general  average  shows  the  small- 
est time  variation  for  the  males  and  the  smallest  distance  varia- 
tion for  the  females.  These  results  do  not  agree  with  those  of 
Yerkes  on  the  dancer.  His  ten  month  (300  day)  dancers  learned 
the  labyrinth  more  rapidly,  the  number  of  trials  required  being 
the  measure  of  learning,  than  those  one  to  two  months  old 
(30-60  days)  while  there  was  no  difference  in  the  learning  abil- 
ity of  the  females  at  the  two  ages.  My  twenty-five  and  sixty- 
five  day  rats  of  both  sexes  formed  the  maze  habit  considerably 
more  rapidly  than  the  three  hundred  day  animals. 

The  fact  that  in  the  number  of  trials,  total  time  and  total 
distance  required  to  learn  the  problem,  the  males  at  sixty-five 
days  are  superior  to  those  at  twenty-five  days  while  the  reverse 
is  true  of  the  females,  suggests  the  possibility  that  the  capacity 
for  habit  formation  develops  earlier  in  the  females  than  in 
the  males. 

DAY  AND  NIGHT  WORK 

It  has  been  stated  by  Slonaker,  and  is  generally  believed, 
that  the  albino  rat  is  nocturnal.  With  a  view  to  testing  this 
matter  certain  rats  in  the  twenty-five  and  two  hundred  day 
groups  were  run  always  in  the  day  time,  certain  others  always 
at  night.  The  averages  for  the  day  and  night  rats  were  ob- 
tained in  the  same  manner  as  the  group  averages,  from  Tables 
A  and  C. 

The  twenty-five  day  rats  run  during  the  day  were  numbers 
1,  2,  4,  5,  6,  15,  16,  17,  19,  20,  21  and  24,  seven  of  which  were 
males  and  six  females.  Those  run  at  night  were  numbers,  8, 
9,  10,  11,  12,  13  and  14,  two  males  and  five  females.  The 


48 


HELEN  B.  HUBBERT 


averages  which  appear  below  in  Table  X  seem  to  show  the  day 
rats  slightly  superior  in  distance  and  trials  while  the  night  rats 
consumed  less  time  and  had  a  slightly  higher  final  efficiency. 
These  differences  are  negligible,  and  there  may  be  said  to  be  no 
difference  in  learning  at  this  age  between  the  rats  run  in  the 
day-time  and  those  run  at  night. 

The  day  group  of  two  hundred  day  rats  consisted  of  two 
males  and  four  females  numbers  18,  19,  20,  21,  23  and  24,  while 
the  night  group  included  two  males  and  four  females  numbered 
6,  7,  8,  9,  10,  15  and  17.  The  averages  show  the  night  group 
to  be  superior  to  the  day  group  in  every  respect  save  that  of 
final  efficiency.  Nevertheless,  we  are  inclined  to  hold  to  our 
previous  statement  that  no  difference  is  shown  in  learning 
ability,  for  the  following  reason:  The  general  average  for  the 
females  of  this  group  was  considerably  higher  than  that  for  the 
males  except  in  the  matter  of  absolute  time.  In  the  day  group 
there  were  only  two  males  and  four  females.  Were  the  number 
of  males  the  same  as  the  number  of  females  it  is  our  belief  that 
the  average  would  be  considerably  lowered  and  the  day  and 
night  groups  prove  to  have  practically  the  same  ability  in  learn- 
ing the  maze  problem. 

TABLE  X 


AVERAGES 

Time 


Trials       Absolute 


Total 


25  days: 
Day.. 

Night. 


200  days: 
Day.. . 

Night.. 


29 
31 


41 
34 


5.5  sec. 

5.4    « 


6.2 
7.2 


207  min. 
159     " 


Distance 


247.4  m. 
261.6  « 


461 
325 


373.5 
"  267.9 


CONTINUATION  OF  WORK  AFTER  THE  PROBLEM  HAS  BEEN  LEARNED 

Another  question  which  interested  us,  was,  what  would  be 
the  effect  •  on  efficiency  if  rats  which  had  learned  the  problem 
were  caused  to  continue  their  runs  in  the  maze  for  a  long  period, 
i.  e.,  would  continued  practice  cause  a  marked  increase  in  effi- 
ciency evinced  by  a  lowering  of  the  absolute  time  record,  or  had 
the  highest  possible  level  already  been  reached  in  the  last  six 
trials  of  the  learning  process  ? 


HABIT  FORMATION  IN  THE  ALBINO  RAT    . 


49 


To  test  the  matter,  six  rats  of  the  sixty-five  day  group  were 
kept  at  work  for  more  than  one  hundred  sixty  trials  after  learn- 
ing was  complete,  the  average  time  for  each  six  trials  was  com- 
puted and  appears  in  Table  XI  as  twenty-seven  tests.  Taken 

TABLE  XI 


Rat8 

Rat  12 

Rat  14 

Rat  15 

Rat 

16 

Rat  17 

Ab.  T. 

6.6 

6.4 

5.9 

5.5 

5.3 

4. 

5 

1 

6. 

7 

7.1 

6.5ee 

5. 

It 

5. 

3 

4. 

Set 

2 

6. 

4f 

7.0 

5.  3ef 

4. 

Set 

4. 

7t 

4. 

5 

3 

5. 

4t 

7.9ee 

4.8t 

4. 

Set 

6. 

9 

e 

6. 

3e 

4 

5. 

2* 

9.4ee 

6.1e 

4. 

1* 

9. 

1 

6. 

Oe 

5 

6. 

7e 

17.  6  eee 

5.8t 

4. 

6t 

6. 

1 

5. 

1 

6 

5. 

8t 

8.5 

S.lf 

4. 

9t 

8. 

8 

10. 

See 

7 

7. 

2e 

6.8e 

5.8t 

7. 

8 

6. 

2 

4. 

See 

8 

5. 

8f 

5.4e* 

5.0et 

5. 

4t 

7. 

9 

e 

4. 

7 

9 

5. 

5ef 

6.4 

5.0* 

6. 

4e 

6. 

1 

4. 

3* 

10 

8. 

2eee 

5.4f 

5.8t 

4. 

3t 

14. 

6 

eeee 

4. 

7 

11 

5. 

2f 

6.  let 

5.5" 

14. 

3e 

5. 

6 

e 

6. 

6e 

12 

6. 

9  eeeee 

5.5f 

4.6" 

4. 

7t 

6. 

5 

e 

4. 

9e 

13 

6.7e 

5.7et 

4.8" 

8. 

2e 

6. 

9 

e 

4. 

4t 

14 

21. 

5  eee 

7.2e 

5.2 

8. 

1 

6. 

2 

4. 

7 

Errors 

15 

13 

5 

5 

9 

8 

15 

6 

See 

8.8 

4.9t 

5. 

ot 

5. 

1 

* 

4. 

7 

16 

lO.Oeee 

6.7e 

5.7et 

19. 

See 

8. 

4 

5. 

4 

17 

14. 

1  eeee 

6.2f 

4.7et 

5. 

6e 

8. 

2 

ee 

5. 

1 

18 

6. 

9ee 

5.7f 

5.4* 

5. 

It 

6. 

7 

4. 

8 

19 

10 

See 

9.9 

5.2" 

5. 

5 

7. 

3 

5. 

4 

20 

5 

9ef 

12.2 

5.2" 

5. 

It 

5. 

7 

4. 

5 

21 

19 

0  eeeee 

7.5 

5.8" 

7. 

7 

22. 

Oe 

8. 

6ee 

22 

11.4eeeee 

9.3e 

8.8 

5. 

6 

24. 

3 

eeee 

7. 

6  eeee 

23 

6 

Set 

7.9e 

5.7et 

12. 

2 

14. 

5 

e 

19. 

9  eeee 

24 

10 

leee 

9.  8  eee 

6.4 

7. 

1 

16. 

1 

eeeee 

6. 

6e 

25 

6.9 

ee 

12.9ee 

6.0 

5.4t              8. 

9 

e 

5. 

4 

26 

11 

5  eeeee 

6.  Of 

5.4  et 

5. 

7 

10. 

4 

e 

6. 

7e 

27 

16 

6ee 

8.  See 

7.1 

5. 

7 

15. 

9 

cccccc 

5. 

1 

28 

8.1 

7.5 

6.8e 

5. 

ot 

18. 

8 

eeee 

6. 

2 

29 

9. 

3 

ee 

30 

7. 

8 

Errors 

37 

10 

5 

3 

27 

12 

e  =  Error 

*  =  Lowest  record  for  individual  rats 

t  =  Lower  record  than  absolute  time  value  for  certain  rat 

The  dotted  line  divides  the  table  into  first  and  second  halves  in  order  to  make 
comparison  of  the  two  stages  easier.  The  number  of  errors  made  by  each  rat  in 
each  half  is  shown. 

individually  the  results  show  that  in  every  case  a  lower  record 
than  the  absolute  time  record  was  made,  but  in  no  case  main- 
tained. If  the  group  average  be  noted,  the  absolute  time  is 
never  quite  reached,  the  curve  (Fig.  8),  starting  a  little  above 


50 


HELEN  B.  HUBBERT 


HABIT  FORMATION  IN  THE  ALBINO  RAT  51 

it  and  continually  rising.  In  other  words,  final  efficiency  de- 
creases rather  than  increases  when  practice  is  continued.  An 
interesting  point  is  that  errors  will  be  made  even  after  the  prob- 
lem is  learned.  Of  the  six  rats  used,  three  made  errors  in  the 
first  test  of  six  trials  after  the  problem  was  learned,  one  in  the 
second  test,  and  one  not  until  the  fifth  test.  Errors  increased 
as  the  work  was  continued.  During  the  last  half  of  the  one 
hundred  sixty  additional  trials  twice  as  many  errors  were  made 
as  in  the  first  half. 

A  closer  examination  of  the  table  shows:  First,  that  the 
best  record  in  each  case  was  made  during  the  first  fourteen 
tests;  Second,  that  the  last  test  was  better  than  the  first  in 
only  one  case  (rat  15) ;  Third,  that  rats  fourteen  and  fifteen 
probably  had  not  reached  their  efficiency  level  during  the  learn- 
ing process,  while  the  other  rats  had.  This  fact  is  deduced 
from  the  number  of  times  each  rat  made  a  record  lower  than 
its  absolute  time  record. 

Rat    8 9  times  out  of  28 

Rat  12 8  times  out  of  28 

Rat  14 21  times  out  of  28 

Rat  15 14  times  out  of  28 

Rat  16 2  times  out  of  28 

Rat  17 3  times  out  of  28 

BLOOD  RELATIONSHIP  AND  LEARNING 

It  was  found  that  the  learning  ability  of  certain  members 
of  a  group  could  be  predicted  from  the  results  obtained  on  other 
members  of  the  same  litter.  The  data  appear  in  Table  XII. 
Three  rats  from  the  Y(CF)  litter  were  used  when  twenty-five 
days  old,  and  five  rats  from  the  same  litter  worked  when  sixty- 
five  days  old.  Two  members  of  the  GJ  litter  learned  the  prob- 
lem at  twenty-five  days,  and  one  at  sixty-five  days.  Two  AL 
rats  worked  when  twenty-five  days  old,  and  one  when  sixty-five 
days  old.  Four  XL  rats  learned  the  problem  at  twenty-five 
days,  three  at  sixty-five  days  and  three  at  two  hundred  days. 

The  rats  belonging  to  the  Y(CF)  litter  required  a  smaller 
number  of  trials  at  twenty-five  days  than  the  average,  but 
their  absolute  time,  total  time  and  total  distance  were  above 
the  average  for  rats  of  that  age.  At  sixty-five  days,  rats  of  the 
same  litter  made  averages  higher  than  the  group  averages  for  that 


52 


HELEN  B.  HUBBERT 


age  except  for  the  absolute  time.  The  GJ  rats  twenty-five 
days  old  had  trial  and  distance  records  higher  than  those  of  the 
entire  group  while  their  absolute  and  total  times  were  less.  The 
same  holds  true  for  the  GJ  rats  at  sixty-five  days  except  that 
their  absolute  time  is  higher.  AL  rats  show  records  lower  than 
the  group  averages  in  every  case  at  twenty-five  days  but  at 
sixty-five  days  all  of  the  AL  averages  are  higher  than  that  for 
the  group. 

Rats  from  the  XL  litter  which  worked  at  twenty-five  days 
made  lower  records  than  the  average  except  in  absolute  time. 
The  same  is  true  of  the  sixty-five  day  members  of  the  same 
litter  and  the  two  hundred  day  XL  rats  have  a  lower  record 
than  the  group  average  in  every  particular. 

In  three  out  of  four  cases  considered  then,  a  high  or  low 
average  at  one  age  seems  to  point  to  the  fact  that  there  will  be  a 
high  or  low  average  for  the  age  or  ages  following. 

It  appears  that  it  is  possible  within  limits  to  predict  the 
capacity  for  habit  formation  of  rats  of  a  certain  litter  at  a  given 
age,  from  the  behavior  of  their  blood  relations  at  any  other  age. 


TABLE  XII 


Time 


Litter 


Age 


Trials       Absolute 


Total 


Distance 


f  25  c 

lays  

25 

5.9 

sec. 

463  i 

nin. 

290.1  n 

I. 

YCF  

65 

a 

40 

5.9 

u 

317 

u 

369.4  ' 

t 

[200 

u 

. 

r  25 

u 

35 

5.3 

u 

140 

u 

319.3 

i 

GJ  

65 

u 

38 

7.6 

a 

136 

u 

284.0 

t 

[200 

u 

.. 

. 

f  25 

u 

23 

5.4 

u 

91 

u 

185.8 

AL  

65 

u 

38 

10.6 

u 

330 

u 

393.2 

1200 

u 

f  25 

u 

34 

5.4 

u 

180 

u 

252.5 

XL  

.  {  65 

u 

24 

8.3 

u 

153 

u 

195.3 

[200 

u 

29 

7.8 

u 

258 

u 

254.4 

f  25 

u 

30 

5.7 

u 

224 

u 

271.6  < 

t 

Gen.  Av  

{  65 

u 

31 

6.8 

u 

318 

u 

260.6  ' 

t 

1200 

u 

42 

8.6 

u 

351 

u 

339.1  ' 

t 

RETENTION 

A  retention  test  was  made  on  five  individuals  of  the  sixty-five 
day  group  who  were  caused  to  relearn  the  problem  after  ninety 
days.  During  this  time  they  were  fed  daily  in  the  maze  except 


HABIT  FORMATION  IN  THE  ALBINO  RAT 


53 


that  at  the  eighty-fifth  day  the  food  supply  was  cut  down,  and 
on  the  eighty-ninth*  day  no  food  at  all  was  allowed.  Probably 
a  better  plan  would  have  been  to  feed  the  rats  in  the  food  box 
of  the  maze  for  a  week  preceding  the  retention  test,  using  the 
same  schedule  employed  in  preliminary  feeding,  and  keeping  the 
food  box  carefully  partitioned  off  from  the  rest  of  the  maze. 

Seventy-six  per  cent  of  the  original  number  of  trials  were 
required  to  relearn,  forty-eight  per  cent  of  the  time  necessary 
for  learning  was  occupied  in  relearning,  and  fifty-two  per  cent 
of  the  original  amount  of  distance  was  covered.  The  absolute 
time  when  learning  was  seven  and  nine  tenths  seconds,  when 
relearning  nine  seconds.  This  difference  probably  being  due  to 
the  increased  age,  since  the  rats  were  approximately  two  hundred 
days  old  at  the  time  of  the  retention  test  and  absolute  time 
increases  with  age. 

Nothing  more  is  shown  by  the  test  on  retention  than  that 
the  interval  between  learning  and  relearning  must  be  made  very 
much  smaller  if  it  is  desired  to  begin  a  problem  with  a  view  to 
determining  the  curve  of  retention. 

The  relation  of  time  to  distance  in  learning,  and  the  matter 
of  elimination  of  alleys  in  the  maze  have  been  discussed  at 
length  in  papers  already  published. 

TABLE  XIII 

LEARNING 
Rat  Trials       Ab.  time       Total  time         Distance 


1 

30 

8.2  sec. 

1327.4  sec.      23033.6  cm. 

2 

54 

7.8 

u 

1651.8 

42368.0 

u 

3 

21 

7.1 

u 

1542.0 

25177.6 

u 

4 

16 

9.8 

u 

496.0 

11603.2 

u 

5 

22 

6.5 

u 

2378.0 

26675.2 

u 

Totals  

143 

39.5 

u 

7395.2 

128857.6 

u 

Averages  

29 

7.9 

u 

1479.1              25771.5 

u 

Rat 


RELEARNING— AFTER  90  DAYS 
Trials       Ab.  time       Total  time 


Distance 


1 

14 

7.  7  sec. 

316.  4  sec.        7264.0 

cm. 

2 

40 

8.7    « 

861.8 

23321.6 

« 

3 

14 

9.2    " 

484.4 

9081.6 

u 

4 

22 

10.3     " 

958.8 

15562.6 

u 

5 

18 

9.3     « 

902.6 

11426.8 

u 

Totals  

108 

45  2     " 

3524  0 

66656  6 

u 

Averages  

22 

9.0     « 

704.8 

13331.3 

u 

54  HELEN  B.  HUBBERT 

RESUME  OF  CONCLUSIONS 

1.  Young  rats  learn  the  maze  more  rapidly  than  the  old 
ones,   the  rapidity  with  which  the  habit  may  be  formed  de- 
creasing with  increase  in  age. 

2.  Absolute  time,  the  time  required  for  the  execution  of  the 
perfect  run,   increases  with  increase  in  age,   the  oldest  group 
requiring  more  than  twice  as  much  time  as  the  youngest. 

3.  The  most  rapid  stage  of  habit  formation  occurs  earlier 
in  the  learning  process  of  the  younger  animals  than  of    the 
older  ones. 

4.  In  the  very  young  rats  (25  days)  and  the  very  old  (300 
days)  sex  differences  are  negligible,  while  among  the  animals  of 
medium  age  (65-300  days)    the  males  learn  more  rapidly  than 
the  females. 

5.  In   general  the   absolute   time  for  the  females  is  lower 
than  that  for  the  males,  suggesting  greater  efficiency  on  the 
part  of  the  former  in  the  execution  of  the  habit  when  it  had  once 
been  perfected. 

6.  Practically  no  difference  in  ability  to  form  the  maze  habit 
is  to  be  found  between  rats  learning  the  problem  in  the  day- 
time and  those  learning  at  night. 

7.  Continued  practice  after  the  problem  has  been  learned 
causes  a  break  in  the  habit  and  does  not  result  in  an  increase 
of  final  efficiency. 

8.  The  rapidity  with  which  the  maze  habit  will  be  formed 
is  predictable,  within  certain  limits,  from  one  family  group  to 
another. 

9.  In  the  matter  of  elimination  of  errors,  the  outer  alleys 
are  usually  those  in  which  useless  movements  are  last  to  drop 
out,  but  a  5-4-3-2  order  does  not  hold,  i.  e.,  errors  in  5  dropping 
out  first,  those  in  4  second,  etc.     This  bears  directly  on  the 
question  of  the  relation  of  the  food  to  the  learning  process  and 
seems  to  negate  the  pleasure-pain  hypothesis,  but  no  conclusive 
evidence  has  been  obtained. 

10.  The  importance  of  an  adequate  test  on  retention  is  made 
quite  evident  by  these  results. 

If  an  analogy  may  be  drawn  between  the  learning  ability 
of  the  rat  and  that  of  the  human  subject,  it  may  be  seen  that 
in  general  the  old  can  learn  a  given  problem  as  well  as  the  young 
although  more  effort  is  required  to  do  so.  The  efficiency  of 


HABIT  FORMATION  IN  THE  ALBINO  RAT  55 

this  learning  can  only  be  measured  by  testing  the  retention 
ability.  Should  such  tests  show  that  the  old  animals  forget 
very  rapidly  and  must  relearn  the  problem  continually  with 
little  or  no  lessening  of  excess  effort,  comparing  unfavorably 
with  the  younger  ones  in  these  respects,  the  above  conclusions 
would  have  to  be  modified.  If,  however,  the  limits  of  retention 
in  the  groups  are  found  to  be  very  nearly  the  same,  and  the 
amount  of  effort  necessary  to  relearn  not  greatly  increased 
for  the  older  group  over  that  for  the  younger,  the  deductions 
would  hold. 


VITA 

Helen  B.  Hubbert,  the  author  of  this  dissertation,  was  born 
at  Lincoln,  Illinois,  June  llth,  1887.  Her  early  education  was 
received  at  the  Preparatory  Department  of  Cumberland  Uni- 
versity and  in  the  Academy  of  Missouri  Valley  College.  In 
1904  she  entered  Missouri  Valley  College,  Marshall,  Missouri, 
from  which  she  graduated  in  1907  with  the  A.B.  degree.  In 
1907-8  she  was  a  graduate  student  at  the  University  of  Penn- 
sylvania. In  1908-9  she  attended  the  Clarke  Training  School 
for  Teachers,  and  from  1909  to  1912  was  a  teacher  in  the  Penn- 
sylvania Institute  for  the  Deaf  at  Mt.  Airy,  Philadelphia,  Pa. 
In  the  fall  of  1912  she  entered  The  Johns  Hopkins  University 
as  a  graduate  student  in  Psychology,  with  Physiology  and 
Psychopathology  as  subordinate  subjects.  She  received  a  uni- 
versity scholarship  in  1912-13,  was  Fellow  in  Psychology  in 
1913-14,  and  held  the  fellowship  of  the  Baltimore  Association 
to  promote  the  University  Education  of  Women  in  1914-15. 


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